algorithms.statistics.formula.formulae¶
Module: algorithms.statistics.formula.formulae¶
Inheritance diagram for nipy.algorithms.statistics.formula.formulae:
Formula objects¶
A formula is basically a sympy expression for the mean of something of the form:
mean = sum([Beta(e)*e for e in expr])
Or, a linear combination of sympy expressions, with each one multiplied by its own “Beta”. The elements of expr can be instances of Term (for a linear regression formula, they would all be instances of Term). But, in general, there might be some other parameters (i.e. sympy.Symbol instances) that are not Terms.
The design matrix is made up of columns that are the derivatives of mean with respect to everything that is not a Term, evaluated at a recarray that has field names given by [str(t) for t in self.terms].
For those familiar with R’s formula syntax, if we wanted a design matrix like the following:
> s.table = read.table("http://www-stat.stanford.edu/~jtaylo/courses/stats191/data/supervisor.table", header=T)
> d = model.matrix(lm(Y ~ X1*X3, s.table)
)
> d
(Intercept) X1 X3 X1:X3
1 1 51 39 1989
2 1 64 54 3456
3 1 70 69 4830
4 1 63 47 2961
5 1 78 66 5148
6 1 55 44 2420
7 1 67 56 3752
8 1 75 55 4125
9 1 82 67 5494
10 1 61 47 2867
11 1 53 58 3074
12 1 60 39 2340
13 1 62 42 2604
14 1 83 45 3735
15 1 77 72 5544
16 1 90 72 6480
17 1 85 69 5865
18 1 60 75 4500
19 1 70 57 3990
20 1 58 54 3132
21 1 40 34 1360
22 1 61 62 3782
23 1 66 50 3300
24 1 37 58 2146
25 1 54 48 2592
26 1 77 63 4851
27 1 75 74 5550
28 1 57 45 2565
29 1 85 71 6035
30 1 82 59 4838
attr(,"assign")
[1] 0 1 2 3
>
With the Formula, it looks like this:
>>> r = np.rec.array([
... (43, 51, 30, 39, 61, 92, 45), (63, 64, 51, 54, 63, 73, 47),
... (71, 70, 68, 69, 76, 86, 48), (61, 63, 45, 47, 54, 84, 35),
... (81, 78, 56, 66, 71, 83, 47), (43, 55, 49, 44, 54, 49, 34),
... (58, 67, 42, 56, 66, 68, 35), (71, 75, 50, 55, 70, 66, 41),
... (72, 82, 72, 67, 71, 83, 31), (67, 61, 45, 47, 62, 80, 41),
... (64, 53, 53, 58, 58, 67, 34), (67, 60, 47, 39, 59, 74, 41),
... (69, 62, 57, 42, 55, 63, 25), (68, 83, 83, 45, 59, 77, 35),
... (77, 77, 54, 72, 79, 77, 46), (81, 90, 50, 72, 60, 54, 36),
... (74, 85, 64, 69, 79, 79, 63), (65, 60, 65, 75, 55, 80, 60),
... (65, 70, 46, 57, 75, 85, 46), (50, 58, 68, 54, 64, 78, 52),
... (50, 40, 33, 34, 43, 64, 33), (64, 61, 52, 62, 66, 80, 41),
... (53, 66, 52, 50, 63, 80, 37), (40, 37, 42, 58, 50, 57, 49),
... (63, 54, 42, 48, 66, 75, 33), (66, 77, 66, 63, 88, 76, 72),
... (78, 75, 58, 74, 80, 78, 49), (48, 57, 44, 45, 51, 83, 38),
... (85, 85, 71, 71, 77, 74, 55), (82, 82, 39, 59, 64, 78, 39)],
... dtype=[('y', '<i8'), ('x1', '<i8'), ('x2', '<i8'),
... ('x3', '<i8'), ('x4', '<i8'), ('x5', '<i8'),
... ('x6', '<i8')])
>>> x1 = Term('x1'); x3 = Term('x3')
>>> f = Formula([x1, x3, x1*x3]) + I
>>> f.mean
_b0*x1 + _b1*x3 + _b2*x1*x3 + _b3
The I is the “intercept” term, I have explicitly not used R’s default of adding it to everything.
>>> f.design(r)
array([(51.0, 39.0, 1989.0, 1.0), (64.0, 54.0, 3456.0, 1.0),
(70.0, 69.0, 4830.0, 1.0), (63.0, 47.0, 2961.0, 1.0),
(78.0, 66.0, 5148.0, 1.0), (55.0, 44.0, 2420.0, 1.0),
(67.0, 56.0, 3752.0, 1.0), (75.0, 55.0, 4125.0, 1.0),
(82.0, 67.0, 5494.0, 1.0), (61.0, 47.0, 2867.0, 1.0),
(53.0, 58.0, 3074.0, 1.0), (60.0, 39.0, 2340.0, 1.0),
(62.0, 42.0, 2604.0, 1.0), (83.0, 45.0, 3735.0, 1.0),
(77.0, 72.0, 5544.0, 1.0), (90.0, 72.0, 6480.0, 1.0),
(85.0, 69.0, 5865.0, 1.0), (60.0, 75.0, 4500.0, 1.0),
(70.0, 57.0, 3990.0, 1.0), (58.0, 54.0, 3132.0, 1.0),
(40.0, 34.0, 1360.0, 1.0), (61.0, 62.0, 3782.0, 1.0),
(66.0, 50.0, 3300.0, 1.0), (37.0, 58.0, 2146.0, 1.0),
(54.0, 48.0, 2592.0, 1.0), (77.0, 63.0, 4851.0, 1.0),
(75.0, 74.0, 5550.0, 1.0), (57.0, 45.0, 2565.0, 1.0),
(85.0, 71.0, 6035.0, 1.0), (82.0, 59.0, 4838.0, 1.0)],
dtype=[('x1', '<f8'), ('x3', '<f8'), ('x1*x3', '<f8'), ('1', '<f8')])
Classes¶
Beta¶
- class nipy.algorithms.statistics.formula.formulae.Beta(name, term)¶
Bases:
DummyA symbol tied to a Term term
- __init__(*args, **kwargs)¶
- adjoint()¶
- apart(x=None, **args)¶
See the apart function in sympy.polys
- property args: tuple[Basic, ...]¶
Returns a tuple of arguments of ‘self’.
Notes
Never use self._args, always use self.args. Only use _args in __new__ when creating a new function. Do not override .args() from Basic (so that it is easy to change the interface in the future if needed).
Examples
>>> from sympy import cot >>> from sympy.abc import x, y
>>> cot(x).args (x,)
>>> cot(x).args[0] x
>>> (x*y).args (x, y)
>>> (x*y).args[1] y
- args_cnc(cset=False, warn=True, split_1=True)¶
Return [commutative factors, non-commutative factors] of self.
Examples
>>> from sympy import symbols, oo >>> A, B = symbols('A B', commutative=0) >>> x, y = symbols('x y') >>> (-2*x*y).args_cnc() [[-1, 2, x, y], []] >>> (-2.5*x).args_cnc() [[-1, 2.5, x], []] >>> (-2*x*A*B*y).args_cnc() [[-1, 2, x, y], [A, B]] >>> (-2*x*A*B*y).args_cnc(split_1=False) [[-2, x, y], [A, B]] >>> (-2*x*y).args_cnc(cset=True) [{-1, 2, x, y}, []]
The arg is always treated as a Mul:
>>> (-2 + x + A).args_cnc() [[], [x - 2 + A]] >>> (-oo).args_cnc() # -oo is a singleton [[-1, oo], []]
- as_base_exp() tuple[Expr, Expr]¶
- as_coeff_Add(rational=False) tuple[Number, Expr]¶
Efficiently extract the coefficient of a summation.
- as_coeff_Mul(rational: bool = False) tuple[Number, Expr]¶
Efficiently extract the coefficient of a product.
- as_coeff_add(*deps) tuple[Expr, tuple[Expr, ...]]¶
Return the tuple (c, args) where self is written as an Add,
a.c should be a Rational added to any terms of the Add that are independent of deps.
args should be a tuple of all other terms of
a; args is empty if self is a Number or if self is independent of deps (when given).This should be used when you do not know if self is an Add or not but you want to treat self as an Add or if you want to process the individual arguments of the tail of self as an Add.
if you know self is an Add and want only the head, use self.args[0];
if you do not want to process the arguments of the tail but need the tail then use self.as_two_terms() which gives the head and tail.
if you want to split self into an independent and dependent parts use
self.as_independent(*deps)
>>> from sympy import S >>> from sympy.abc import x, y >>> (S(3)).as_coeff_add() (3, ()) >>> (3 + x).as_coeff_add() (3, (x,)) >>> (3 + x + y).as_coeff_add(x) (y + 3, (x,)) >>> (3 + y).as_coeff_add(x) (y + 3, ())
- as_coeff_exponent(x) tuple[Expr, Expr]¶
c*x**e -> c,ewhere x can be any symbolic expression.
- as_coeff_mul(*deps, **kwargs) tuple[Expr, tuple[Expr, ...]]¶
Return the tuple (c, args) where self is written as a Mul,
m.c should be a Rational multiplied by any factors of the Mul that are independent of deps.
args should be a tuple of all other factors of m; args is empty if self is a Number or if self is independent of deps (when given).
This should be used when you do not know if self is a Mul or not but you want to treat self as a Mul or if you want to process the individual arguments of the tail of self as a Mul.
if you know self is a Mul and want only the head, use self.args[0];
if you do not want to process the arguments of the tail but need the tail then use self.as_two_terms() which gives the head and tail;
if you want to split self into an independent and dependent parts use
self.as_independent(*deps)
>>> from sympy import S >>> from sympy.abc import x, y >>> (S(3)).as_coeff_mul() (3, ()) >>> (3*x*y).as_coeff_mul() (3, (x, y)) >>> (3*x*y).as_coeff_mul(x) (3*y, (x,)) >>> (3*y).as_coeff_mul(x) (3*y, ())
- as_coefficient(expr)¶
Extracts symbolic coefficient at the given expression. In other words, this functions separates ‘self’ into the product of ‘expr’ and ‘expr’-free coefficient. If such separation is not possible it will return None.
See also
coeffreturn sum of terms have a given factor
as_coeff_Addseparate the additive constant from an expression
as_coeff_Mulseparate the multiplicative constant from an expression
as_independentseparate x-dependent terms/factors from others
sympy.polys.polytools.Poly.coeff_monomialefficiently find the single coefficient of a monomial in Poly
sympy.polys.polytools.Poly.nthlike coeff_monomial but powers of monomial terms are used
Examples
>>> from sympy import E, pi, sin, I, Poly >>> from sympy.abc import x
>>> E.as_coefficient(E) 1 >>> (2*E).as_coefficient(E) 2 >>> (2*sin(E)*E).as_coefficient(E)
Two terms have E in them so a sum is returned. (If one were desiring the coefficient of the term exactly matching E then the constant from the returned expression could be selected. Or, for greater precision, a method of Poly can be used to indicate the desired term from which the coefficient is desired.)
>>> (2*E + x*E).as_coefficient(E) x + 2 >>> _.args[0] # just want the exact match 2 >>> p = Poly(2*E + x*E); p Poly(x*E + 2*E, x, E, domain='ZZ') >>> p.coeff_monomial(E) 2 >>> p.nth(0, 1) 2
Since the following cannot be written as a product containing E as a factor, None is returned. (If the coefficient
2*xis desired then thecoeffmethod should be used.)>>> (2*E*x + x).as_coefficient(E) >>> (2*E*x + x).coeff(E) 2*x
>>> (E*(x + 1) + x).as_coefficient(E)
>>> (2*pi*I).as_coefficient(pi*I) 2 >>> (2*I).as_coefficient(pi*I)
- as_coefficients_dict(*syms)¶
Return a dictionary mapping terms to their Rational coefficient. Since the dictionary is a defaultdict, inquiries about terms which were not present will return a coefficient of 0.
If symbols
symsare provided, any multiplicative terms independent of them will be considered a coefficient and a regular dictionary of syms-dependent generators as keys and their corresponding coefficients as values will be returned.Examples
>>> from sympy.abc import a, x, y >>> (3*x + a*x + 4).as_coefficients_dict() {1: 4, x: 3, a*x: 1} >>> _[a] 0 >>> (3*a*x).as_coefficients_dict() {a*x: 3} >>> (3*a*x).as_coefficients_dict(x) {x: 3*a} >>> (3*a*x).as_coefficients_dict(y) {1: 3*a*x}
- as_content_primitive(radical=False, clear=True)¶
This method should recursively remove a Rational from all arguments and return that (content) and the new self (primitive). The content should always be positive and
Mul(*foo.as_content_primitive()) == foo. The primitive need not be in canonical form and should try to preserve the underlying structure if possible (i.e. expand_mul should not be applied to self).Examples
>>> from sympy import sqrt >>> from sympy.abc import x, y, z
>>> eq = 2 + 2*x + 2*y*(3 + 3*y)
The as_content_primitive function is recursive and retains structure:
>>> eq.as_content_primitive() (2, x + 3*y*(y + 1) + 1)
Integer powers will have Rationals extracted from the base:
>>> ((2 + 6*x)**2).as_content_primitive() (4, (3*x + 1)**2) >>> ((2 + 6*x)**(2*y)).as_content_primitive() (1, (2*(3*x + 1))**(2*y))
Terms may end up joining once their as_content_primitives are added:
>>> ((5*(x*(1 + y)) + 2*x*(3 + 3*y))).as_content_primitive() (11, x*(y + 1)) >>> ((3*(x*(1 + y)) + 2*x*(3 + 3*y))).as_content_primitive() (9, x*(y + 1)) >>> ((3*(z*(1 + y)) + 2.0*x*(3 + 3*y))).as_content_primitive() (1, 6.0*x*(y + 1) + 3*z*(y + 1)) >>> ((5*(x*(1 + y)) + 2*x*(3 + 3*y))**2).as_content_primitive() (121, x**2*(y + 1)**2) >>> ((x*(1 + y) + 0.4*x*(3 + 3*y))**2).as_content_primitive() (1, 4.84*x**2*(y + 1)**2)
Radical content can also be factored out of the primitive:
>>> (2*sqrt(2) + 4*sqrt(10)).as_content_primitive(radical=True) (2, sqrt(2)*(1 + 2*sqrt(5)))
If clear=False (default is True) then content will not be removed from an Add if it can be distributed to leave one or more terms with integer coefficients.
>>> (x/2 + y).as_content_primitive() (1/2, x + 2*y) >>> (x/2 + y).as_content_primitive(clear=False) (1, x/2 + y)
- as_dummy()¶
Return the expression with any objects having structurally bound symbols replaced with unique, canonical symbols within the object in which they appear and having only the default assumption for commutativity being True. When applied to a symbol a new symbol having only the same commutativity will be returned.
Notes
Any object that has structurally bound variables should have a property, bound_symbols that returns those symbols appearing in the object.
Examples
>>> from sympy import Integral, Symbol >>> from sympy.abc import x >>> r = Symbol('r', real=True) >>> Integral(r, (r, x)).as_dummy() Integral(_0, (_0, x)) >>> _.variables[0].is_real is None True >>> r.as_dummy() _r
- as_expr(*gens)¶
Convert a polynomial to a SymPy expression.
Examples
>>> from sympy import sin >>> from sympy.abc import x, y
>>> f = (x**2 + x*y).as_poly(x, y) >>> f.as_expr() x**2 + x*y
>>> sin(x).as_expr() sin(x)
- as_independent(*deps, **hint) tuple[Expr, Expr]¶
A mostly naive separation of a Mul or Add into arguments that are not are dependent on deps. To obtain as complete a separation of variables as possible, use a separation method first, e.g.:
separatevars() to change Mul, Add and Pow (including exp) into Mul
.expand(mul=True) to change Add or Mul into Add
.expand(log=True) to change log expr into an Add
The only non-naive thing that is done here is to respect noncommutative ordering of variables and to always return (0, 0) for self of zero regardless of hints.
For nonzero self, the returned tuple (i, d) has the following interpretation:
i will has no variable that appears in deps
d will either have terms that contain variables that are in deps, or be equal to 0 (when self is an Add) or 1 (when self is a Mul)
if self is an Add then self = i + d
if self is a Mul then self = i*d
otherwise (self, S.One) or (S.One, self) is returned.
To force the expression to be treated as an Add, use the hint as_Add=True
See also
separatevarsexpand_logsympy.core.add.Add.as_two_termssympy.core.mul.Mul.as_two_termsas_coeff_mul
Examples
– self is an Add
>>> from sympy import sin, cos, exp >>> from sympy.abc import x, y, z
>>> (x + x*y).as_independent(x) (0, x*y + x) >>> (x + x*y).as_independent(y) (x, x*y) >>> (2*x*sin(x) + y + x + z).as_independent(x) (y + z, 2*x*sin(x) + x) >>> (2*x*sin(x) + y + x + z).as_independent(x, y) (z, 2*x*sin(x) + x + y)
– self is a Mul
>>> (x*sin(x)*cos(y)).as_independent(x) (cos(y), x*sin(x))
non-commutative terms cannot always be separated out when self is a Mul
>>> from sympy import symbols >>> n1, n2, n3 = symbols('n1 n2 n3', commutative=False) >>> (n1 + n1*n2).as_independent(n2) (n1, n1*n2) >>> (n2*n1 + n1*n2).as_independent(n2) (0, n1*n2 + n2*n1) >>> (n1*n2*n3).as_independent(n1) (1, n1*n2*n3) >>> (n1*n2*n3).as_independent(n2) (n1, n2*n3) >>> ((x-n1)*(x-y)).as_independent(x) (1, (x - y)*(x - n1))
– self is anything else:
>>> (sin(x)).as_independent(x) (1, sin(x)) >>> (sin(x)).as_independent(y) (sin(x), 1) >>> exp(x+y).as_independent(x) (1, exp(x + y))
– force self to be treated as an Add:
>>> (3*x).as_independent(x, as_Add=True) (0, 3*x)
– force self to be treated as a Mul:
>>> (3+x).as_independent(x, as_Add=False) (1, x + 3) >>> (-3+x).as_independent(x, as_Add=False) (1, x - 3)
Note how the below differs from the above in making the constant on the dep term positive.
>>> (y*(-3+x)).as_independent(x) (y, x - 3)
- – use .as_independent() for true independence testing instead
of .has(). The former considers only symbols in the free symbols while the latter considers all symbols
>>> from sympy import Integral >>> I = Integral(x, (x, 1, 2)) >>> I.has(x) True >>> x in I.free_symbols False >>> I.as_independent(x) == (I, 1) True >>> (I + x).as_independent(x) == (I, x) True
Note: when trying to get independent terms, a separation method might need to be used first. In this case, it is important to keep track of what you send to this routine so you know how to interpret the returned values
>>> from sympy import separatevars, log >>> separatevars(exp(x+y)).as_independent(x) (exp(y), exp(x)) >>> (x + x*y).as_independent(y) (x, x*y) >>> separatevars(x + x*y).as_independent(y) (x, y + 1) >>> (x*(1 + y)).as_independent(y) (x, y + 1) >>> (x*(1 + y)).expand(mul=True).as_independent(y) (x, x*y) >>> a, b=symbols('a b', positive=True) >>> (log(a*b).expand(log=True)).as_independent(b) (log(a), log(b))
- as_leading_term(*symbols, logx=None, cdir=0)¶
Returns the leading (nonzero) term of the series expansion of self.
The _eval_as_leading_term routines are used to do this, and they must always return a non-zero value.
Examples
>>> from sympy.abc import x >>> (1 + x + x**2).as_leading_term(x) 1 >>> (1/x**2 + x + x**2).as_leading_term(x) x**(-2)
- as_numer_denom()¶
Return the numerator and the denominator of an expression.
expression -> a/b -> a, b
This is just a stub that should be defined by an object’s class methods to get anything else.
See also
normalreturn
a/binstead of(a, b)
- as_ordered_factors(order=None)¶
Return list of ordered factors (if Mul) else [self].
- as_ordered_terms(order=None, data=False)¶
Transform an expression to an ordered list of terms.
Examples
>>> from sympy import sin, cos >>> from sympy.abc import x
>>> (sin(x)**2*cos(x) + sin(x)**2 + 1).as_ordered_terms() [sin(x)**2*cos(x), sin(x)**2, 1]
- as_poly(*gens, **args)¶
Converts
selfto a polynomial or returnsNone.
- as_powers_dict()¶
Return self as a dictionary of factors with each factor being treated as a power. The keys are the bases of the factors and the values, the corresponding exponents. The resulting dictionary should be used with caution if the expression is a Mul and contains non- commutative factors since the order that they appeared will be lost in the dictionary.
See also
as_ordered_factorsAn alternative for noncommutative applications, returning an ordered list of factors.
args_cncSimilar to as_ordered_factors, but guarantees separation of commutative and noncommutative factors.
- as_real_imag(deep=True, **hints)¶
Performs complex expansion on ‘self’ and returns a tuple containing collected both real and imaginary parts. This method cannot be confused with re() and im() functions, which does not perform complex expansion at evaluation.
However it is possible to expand both re() and im() functions and get exactly the same results as with a single call to this function.
>>> from sympy import symbols, I
>>> x, y = symbols('x,y', real=True)
>>> (x + y*I).as_real_imag() (x, y)
>>> from sympy.abc import z, w
>>> (z + w*I).as_real_imag() (re(z) - im(w), re(w) + im(z))
- as_set()¶
Rewrites Boolean expression in terms of real sets.
Examples
>>> from sympy import Symbol, Eq, Or, And >>> x = Symbol('x', real=True) >>> Eq(x, 0).as_set() {0} >>> (x > 0).as_set() Interval.open(0, oo) >>> And(-2 < x, x < 2).as_set() Interval.open(-2, 2) >>> Or(x < -2, 2 < x).as_set() Union(Interval.open(-oo, -2), Interval.open(2, oo))
- as_terms()¶
Transform an expression to a list of terms.
- aseries(x=None, n=6, bound=0, hir=False)¶
Asymptotic Series expansion of self. This is equivalent to
self.series(x, oo, n).- Parameters:
- selfExpression
The expression whose series is to be expanded.
- xSymbol
It is the variable of the expression to be calculated.
- nValue
The value used to represent the order in terms of
x**n, up to which the series is to be expanded.- hirBoolean
Set this parameter to be True to produce hierarchical series. It stops the recursion at an early level and may provide nicer and more useful results.
- boundValue, Integer
Use the
boundparameter to give limit on rewriting coefficients in its normalised form.
- Returns:
- Expr
Asymptotic series expansion of the expression.
See also
Expr.aseriesSee the docstring of this function for complete details of this wrapper.
Notes
This algorithm is directly induced from the limit computational algorithm provided by Gruntz. It majorly uses the mrv and rewrite sub-routines. The overall idea of this algorithm is first to look for the most rapidly varying subexpression w of a given expression f and then expands f in a series in w. Then same thing is recursively done on the leading coefficient till we get constant coefficients.
If the most rapidly varying subexpression of a given expression f is f itself, the algorithm tries to find a normalised representation of the mrv set and rewrites f using this normalised representation.
If the expansion contains an order term, it will be either
O(x ** (-n))orO(w ** (-n))wherewbelongs to the most rapidly varying expression ofself.References
[1]Gruntz, Dominik. A new algorithm for computing asymptotic series. In: Proc. 1993 Int. Symp. Symbolic and Algebraic Computation. 1993. pp. 239-244.
[2]Gruntz thesis - p90
Examples
>>> from sympy import sin, exp >>> from sympy.abc import x
>>> e = sin(1/x + exp(-x)) - sin(1/x)
>>> e.aseries(x) (1/(24*x**4) - 1/(2*x**2) + 1 + O(x**(-6), (x, oo)))*exp(-x)
>>> e.aseries(x, n=3, hir=True) -exp(-2*x)*sin(1/x)/2 + exp(-x)*cos(1/x) + O(exp(-3*x), (x, oo))
>>> e = exp(exp(x)/(1 - 1/x))
>>> e.aseries(x) exp(exp(x)/(1 - 1/x))
>>> e.aseries(x, bound=3) exp(exp(x)/x**2)*exp(exp(x)/x)*exp(-exp(x) + exp(x)/(1 - 1/x) - exp(x)/x - exp(x)/x**2)*exp(exp(x))
For rational expressions this method may return original expression without the Order term. >>> (1/x).aseries(x, n=8) 1/x
- property assumptions0¶
Return object type assumptions.
For example:
Symbol(‘x’, real=True) Symbol(‘x’, integer=True)
are different objects. In other words, besides Python type (Symbol in this case), the initial assumptions are also forming their typeinfo.
Examples
>>> from sympy import Symbol >>> from sympy.abc import x >>> x.assumptions0 {'commutative': True} >>> x = Symbol("x", positive=True) >>> x.assumptions0 {'commutative': True, 'complex': True, 'extended_negative': False, 'extended_nonnegative': True, 'extended_nonpositive': False, 'extended_nonzero': True, 'extended_positive': True, 'extended_real': True, 'finite': True, 'hermitian': True, 'imaginary': False, 'infinite': False, 'negative': False, 'nonnegative': True, 'nonpositive': False, 'nonzero': True, 'positive': True, 'real': True, 'zero': False}
- atoms(*types)¶
Returns the atoms that form the current object.
By default, only objects that are truly atomic and cannot be divided into smaller pieces are returned: symbols, numbers, and number symbols like I and pi. It is possible to request atoms of any type, however, as demonstrated below.
Examples
>>> from sympy import I, pi, sin >>> from sympy.abc import x, y >>> (1 + x + 2*sin(y + I*pi)).atoms() {1, 2, I, pi, x, y}
If one or more types are given, the results will contain only those types of atoms.
>>> from sympy import Number, NumberSymbol, Symbol >>> (1 + x + 2*sin(y + I*pi)).atoms(Symbol) {x, y}
>>> (1 + x + 2*sin(y + I*pi)).atoms(Number) {1, 2}
>>> (1 + x + 2*sin(y + I*pi)).atoms(Number, NumberSymbol) {1, 2, pi}
>>> (1 + x + 2*sin(y + I*pi)).atoms(Number, NumberSymbol, I) {1, 2, I, pi}
Note that I (imaginary unit) and zoo (complex infinity) are special types of number symbols and are not part of the NumberSymbol class.
The type can be given implicitly, too:
>>> (1 + x + 2*sin(y + I*pi)).atoms(x) # x is a Symbol {x, y}
Be careful to check your assumptions when using the implicit option since
S(1).is_Integer = Truebuttype(S(1))isOne, a special type of SymPy atom, whiletype(S(2))is typeIntegerand will find all integers in an expression:>>> from sympy import S >>> (1 + x + 2*sin(y + I*pi)).atoms(S(1)) {1}
>>> (1 + x + 2*sin(y + I*pi)).atoms(S(2)) {1, 2}
Finally, arguments to atoms() can select more than atomic atoms: any SymPy type (loaded in core/__init__.py) can be listed as an argument and those types of “atoms” as found in scanning the arguments of the expression recursively:
>>> from sympy import Function, Mul >>> from sympy.core.function import AppliedUndef >>> f = Function('f') >>> (1 + f(x) + 2*sin(y + I*pi)).atoms(Function) {f(x), sin(y + I*pi)} >>> (1 + f(x) + 2*sin(y + I*pi)).atoms(AppliedUndef) {f(x)}
>>> (1 + x + 2*sin(y + I*pi)).atoms(Mul) {I*pi, 2*sin(y + I*pi)}
- property binary_symbols¶
Return from the atoms of self those which are free symbols.
Not all free symbols are
Symbol. Eg: IndexedBase(‘I’)[0].free_symbolsFor most expressions, all symbols are free symbols. For some classes this is not true. e.g. Integrals use Symbols for the dummy variables which are bound variables, so Integral has a method to return all symbols except those. Derivative keeps track of symbols with respect to which it will perform a derivative; those are bound variables, too, so it has its own free_symbols method.
Any other method that uses bound variables should implement a free_symbols method.
- cancel(*gens, **args)¶
See the cancel function in sympy.polys
- property canonical_variables¶
Return a dictionary mapping any variable defined in
self.bound_symbolsto Symbols that do not clash with any free symbols in the expression.Examples
>>> from sympy import Lambda >>> from sympy.abc import x >>> Lambda(x, 2*x).canonical_variables {x: _0}
- classmethod class_key()¶
Nice order of classes.
- coeff(x, n=1, right=False, _first=True)¶
Returns the coefficient from the term(s) containing
x**n. Ifnis zero then all terms independent ofxwill be returned.See also
as_coefficientseparate the expression into a coefficient and factor
as_coeff_Addseparate the additive constant from an expression
as_coeff_Mulseparate the multiplicative constant from an expression
as_independentseparate x-dependent terms/factors from others
sympy.polys.polytools.Poly.coeff_monomialefficiently find the single coefficient of a monomial in Poly
sympy.polys.polytools.Poly.nthlike coeff_monomial but powers of monomial terms are used
Examples
>>> from sympy import symbols >>> from sympy.abc import x, y, z
You can select terms that have an explicit negative in front of them:
>>> (-x + 2*y).coeff(-1) x >>> (x - 2*y).coeff(-1) 2*y
You can select terms with no Rational coefficient:
>>> (x + 2*y).coeff(1) x >>> (3 + 2*x + 4*x**2).coeff(1) 0
You can select terms independent of x by making n=0; in this case expr.as_independent(x)[0] is returned (and 0 will be returned instead of None):
>>> (3 + 2*x + 4*x**2).coeff(x, 0) 3 >>> eq = ((x + 1)**3).expand() + 1 >>> eq x**3 + 3*x**2 + 3*x + 2 >>> [eq.coeff(x, i) for i in reversed(range(4))] [1, 3, 3, 2] >>> eq -= 2 >>> [eq.coeff(x, i) for i in reversed(range(4))] [1, 3, 3, 0]
You can select terms that have a numerical term in front of them:
>>> (-x - 2*y).coeff(2) -y >>> from sympy import sqrt >>> (x + sqrt(2)*x).coeff(sqrt(2)) x
The matching is exact:
>>> (3 + 2*x + 4*x**2).coeff(x) 2 >>> (3 + 2*x + 4*x**2).coeff(x**2) 4 >>> (3 + 2*x + 4*x**2).coeff(x**3) 0 >>> (z*(x + y)**2).coeff((x + y)**2) z >>> (z*(x + y)**2).coeff(x + y) 0
In addition, no factoring is done, so 1 + z*(1 + y) is not obtained from the following:
>>> (x + z*(x + x*y)).coeff(x) 1
If such factoring is desired, factor_terms can be used first:
>>> from sympy import factor_terms >>> factor_terms(x + z*(x + x*y)).coeff(x) z*(y + 1) + 1
>>> n, m, o = symbols('n m o', commutative=False) >>> n.coeff(n) 1 >>> (3*n).coeff(n) 3 >>> (n*m + m*n*m).coeff(n) # = (1 + m)*n*m 1 + m >>> (n*m + m*n*m).coeff(n, right=True) # = (1 + m)*n*m m
If there is more than one possible coefficient 0 is returned:
>>> (n*m + m*n).coeff(n) 0
If there is only one possible coefficient, it is returned:
>>> (n*m + x*m*n).coeff(m*n) x >>> (n*m + x*m*n).coeff(m*n, right=1) 1
- collect(syms, func=None, evaluate=True, exact=False, distribute_order_term=True)¶
See the collect function in sympy.simplify
- combsimp()¶
See the combsimp function in sympy.simplify
- compare(other)¶
Return -1, 0, 1 if the object is smaller, equal, or greater than other.
Not in the mathematical sense. If the object is of a different type from the “other” then their classes are ordered according to the sorted_classes list.
Examples
>>> from sympy.abc import x, y >>> x.compare(y) -1 >>> x.compare(x) 0 >>> y.compare(x) 1
- compute_leading_term(x, logx=None)¶
Deprecated function to compute the leading term of a series.
as_leading_term is only allowed for results of .series() This is a wrapper to compute a series first.
- conjugate()¶
Returns the complex conjugate of ‘self’.
- copy()¶
- could_extract_minus_sign()¶
Return True if self has -1 as a leading factor or has more literal negative signs than positive signs in a sum, otherwise False.
Examples
>>> from sympy.abc import x, y >>> e = x - y >>> {i.could_extract_minus_sign() for i in (e, -e)} {False, True}
Though the
y - xis considered like-(x - y), since it is in a product without a leading factor of -1, the result is false below:>>> (x*(y - x)).could_extract_minus_sign() False
To put something in canonical form wrt to sign, use signsimp:
>>> from sympy import signsimp >>> signsimp(x*(y - x)) -x*(x - y) >>> _.could_extract_minus_sign() True
- count(query)¶
Count the number of matching subexpressions.
- count_ops(visual=None)¶
Wrapper for count_ops that returns the operation count.
- default_assumptions = {}¶
- diff(*symbols, **assumptions)¶
- dir(x, cdir)¶
- doit(**hints)¶
Evaluate objects that are not evaluated by default like limits, integrals, sums and products. All objects of this kind will be evaluated recursively, unless some species were excluded via ‘hints’ or unless the ‘deep’ hint was set to ‘False’.
>>> from sympy import Integral >>> from sympy.abc import x
>>> 2*Integral(x, x) 2*Integral(x, x)
>>> (2*Integral(x, x)).doit() x**2
>>> (2*Integral(x, x)).doit(deep=False) 2*Integral(x, x)
- dummy_eq(other, symbol=None)¶
Compare two expressions and handle dummy symbols.
Examples
>>> from sympy import Dummy >>> from sympy.abc import x, y
>>> u = Dummy('u')
>>> (u**2 + 1).dummy_eq(x**2 + 1) True >>> (u**2 + 1) == (x**2 + 1) False
>>> (u**2 + y).dummy_eq(x**2 + y, x) True >>> (u**2 + y).dummy_eq(x**2 + y, y) False
- dummy_index¶
- equals(other, failing_expression=False)¶
Return True if self == other, False if it does not, or None. If failing_expression is True then the expression which did not simplify to a 0 will be returned instead of None.
- evalf(n=15, subs=None, maxn=100, chop=False, strict=False, quad=None, verbose=False)¶
Evaluate the given formula to an accuracy of n digits.
- Parameters:
- subsdict, optional
Substitute numerical values for symbols, e.g.
subs={x:3, y:1+pi}. The substitutions must be given as a dictionary.- maxnint, optional
Allow a maximum temporary working precision of maxn digits.
- chopbool or number, optional
Specifies how to replace tiny real or imaginary parts in subresults by exact zeros.
When
Truethe chop value defaults to standard precision.Otherwise the chop value is used to determine the magnitude of “small” for purposes of chopping.
>>> from sympy import N >>> x = 1e-4 >>> N(x, chop=True) 0.000100000000000000 >>> N(x, chop=1e-5) 0.000100000000000000 >>> N(x, chop=1e-4) 0
- strictbool, optional
Raise
PrecisionExhaustedif any subresult fails to evaluate to full accuracy, given the available maxprec.- quadstr, optional
Choose algorithm for numerical quadrature. By default, tanh-sinh quadrature is used. For oscillatory integrals on an infinite interval, try
quad='osc'.- verbosebool, optional
Print debug information.
Notes
When Floats are naively substituted into an expression, precision errors may adversely affect the result. For example, adding 1e16 (a Float) to 1 will truncate to 1e16; if 1e16 is then subtracted, the result will be 0. That is exactly what happens in the following:
>>> from sympy.abc import x, y, z >>> values = {x: 1e16, y: 1, z: 1e16} >>> (x + y - z).subs(values) 0
Using the subs argument for evalf is the accurate way to evaluate such an expression:
>>> (x + y - z).evalf(subs=values) 1.00000000000000
- expand(deep=True, modulus=None, power_base=True, power_exp=True, mul=True, log=True, multinomial=True, basic=True, **hints)¶
Expand an expression using hints.
See the docstring of the expand() function in sympy.core.function for more information.
- property expr_free_symbols¶
Like
free_symbols, but returns the free symbols only if they are contained in an expression node.Examples
>>> from sympy.abc import x, y >>> (x + y).expr_free_symbols {x, y}
If the expression is contained in a non-expression object, do not return the free symbols. Compare:
>>> from sympy import Tuple >>> t = Tuple(x + y) >>> t.expr_free_symbols set() >>> t.free_symbols {x, y}
- extract_additively(c)¶
Return self - c if it’s possible to subtract c from self and make all matching coefficients move towards zero, else return None.
See also
Examples
>>> from sympy.abc import x, y >>> e = 2*x + 3 >>> e.extract_additively(x + 1) x + 2 >>> e.extract_additively(3*x) >>> e.extract_additively(4) >>> (y*(x + 1)).extract_additively(x + 1) >>> ((x + 1)*(x + 2*y + 1) + 3).extract_additively(x + 1) (x + 1)*(x + 2*y) + 3
- extract_branch_factor(allow_half=False)¶
Try to write self as
exp_polar(2*pi*I*n)*zin a nice way. Return (z, n).>>> from sympy import exp_polar, I, pi >>> from sympy.abc import x, y >>> exp_polar(I*pi).extract_branch_factor() (exp_polar(I*pi), 0) >>> exp_polar(2*I*pi).extract_branch_factor() (1, 1) >>> exp_polar(-pi*I).extract_branch_factor() (exp_polar(I*pi), -1) >>> exp_polar(3*pi*I + x).extract_branch_factor() (exp_polar(x + I*pi), 1) >>> (y*exp_polar(-5*pi*I)*exp_polar(3*pi*I + 2*pi*x)).extract_branch_factor() (y*exp_polar(2*pi*x), -1) >>> exp_polar(-I*pi/2).extract_branch_factor() (exp_polar(-I*pi/2), 0)
If allow_half is True, also extract exp_polar(I*pi):
>>> exp_polar(I*pi).extract_branch_factor(allow_half=True) (1, 1/2) >>> exp_polar(2*I*pi).extract_branch_factor(allow_half=True) (1, 1) >>> exp_polar(3*I*pi).extract_branch_factor(allow_half=True) (1, 3/2) >>> exp_polar(-I*pi).extract_branch_factor(allow_half=True) (1, -1/2)
- extract_multiplicatively(c)¶
Return None if it’s not possible to make self in the form c * something in a nice way, i.e. preserving the properties of arguments of self.
Examples
>>> from sympy import symbols, Rational
>>> x, y = symbols('x,y', real=True)
>>> ((x*y)**3).extract_multiplicatively(x**2 * y) x*y**2
>>> ((x*y)**3).extract_multiplicatively(x**4 * y)
>>> (2*x).extract_multiplicatively(2) x
>>> (2*x).extract_multiplicatively(3)
>>> (Rational(1, 2)*x).extract_multiplicatively(3) x/6
- factor(*gens, **args)¶
See the factor() function in sympy.polys.polytools
- find(query, group=False)¶
Find all subexpressions matching a query.
- fourier_series(limits=None)¶
Compute fourier sine/cosine series of self.
See the docstring of the
fourier_series()in sympy.series.fourier for more information.
- fps(x=None, x0=0, dir=1, hyper=True, order=4, rational=True, full=False)¶
Compute formal power power series of self.
See the docstring of the
fps()function in sympy.series.formal for more information.
- property free_symbols¶
Return from the atoms of self those which are free symbols.
Not all free symbols are
Symbol. Eg: IndexedBase(‘I’)[0].free_symbolsFor most expressions, all symbols are free symbols. For some classes this is not true. e.g. Integrals use Symbols for the dummy variables which are bound variables, so Integral has a method to return all symbols except those. Derivative keeps track of symbols with respect to which it will perform a derivative; those are bound variables, too, so it has its own free_symbols method.
Any other method that uses bound variables should implement a free_symbols method.
- classmethod fromiter(args, **assumptions)¶
Create a new object from an iterable.
This is a convenience function that allows one to create objects from any iterable, without having to convert to a list or tuple first.
Examples
>>> from sympy import Tuple >>> Tuple.fromiter(i for i in range(5)) (0, 1, 2, 3, 4)
- property func¶
The top-level function in an expression.
The following should hold for all objects:
>> x == x.func(*x.args)
Examples
>>> from sympy.abc import x >>> a = 2*x >>> a.func <class 'sympy.core.mul.Mul'> >>> a.args (2, x) >>> a.func(*a.args) 2*x >>> a == a.func(*a.args) True
- gammasimp()¶
See the gammasimp function in sympy.simplify
- getO()¶
Returns the additive O(..) symbol if there is one, else None.
- getn()¶
Returns the order of the expression.
Examples
>>> from sympy import O >>> from sympy.abc import x >>> (1 + x + O(x**2)).getn() 2 >>> (1 + x).getn()
- has(*patterns)¶
Test whether any subexpression matches any of the patterns.
Examples
>>> from sympy import sin >>> from sympy.abc import x, y, z >>> (x**2 + sin(x*y)).has(z) False >>> (x**2 + sin(x*y)).has(x, y, z) True >>> x.has(x) True
Note
hasis a structural algorithm with no knowledge of mathematics. Consider the following half-open interval:>>> from sympy import Interval >>> i = Interval.Lopen(0, 5); i Interval.Lopen(0, 5) >>> i.args (0, 5, True, False) >>> i.has(4) # there is no "4" in the arguments False >>> i.has(0) # there *is* a "0" in the arguments True
Instead, use
containsto determine whether a number is in the interval or not:>>> i.contains(4) True >>> i.contains(0) False
Note that
expr.has(*patterns)is exactly equivalent toany(expr.has(p) for p in patterns). In particular,Falseis returned when the list of patterns is empty.>>> x.has() False
- has_free(*patterns)¶
Return True if self has object(s)
xas a free expression else False.Examples
>>> from sympy import Integral, Function >>> from sympy.abc import x, y >>> f = Function('f') >>> g = Function('g') >>> expr = Integral(f(x), (f(x), 1, g(y))) >>> expr.free_symbols {y} >>> expr.has_free(g(y)) True >>> expr.has_free(*(x, f(x))) False
This works for subexpressions and types, too:
>>> expr.has_free(g) True >>> (x + y + 1).has_free(y + 1) True
- has_xfree(s: set[Basic])¶
Return True if self has any of the patterns in s as a free argument, else False. This is like Basic.has_free but this will only report exact argument matches.
Examples
>>> from sympy import Function >>> from sympy.abc import x, y >>> f = Function('f') >>> f(x).has_xfree({f}) False >>> f(x).has_xfree({f(x)}) True >>> f(x + 1).has_xfree({x}) True >>> f(x + 1).has_xfree({x + 1}) True >>> f(x + y + 1).has_xfree({x + 1}) False
- integrate(*args, **kwargs)¶
See the integrate function in sympy.integrals
- invert(g, *gens, **args)¶
Return the multiplicative inverse of
selfmodgwhereself(andg) may be symbolic expressions).See also
sympy.core.numbers.mod_inverse,sympy.polys.polytools.invert
- is_Add = False¶
- is_AlgebraicNumber = False¶
- is_Atom = True¶
- is_Boolean = False¶
- is_Derivative = False¶
- is_Dummy = True¶
- is_Equality = False¶
- is_Float = False¶
- is_Function = False¶
- is_Indexed = False¶
- is_Integer = False¶
- is_MatAdd = False¶
- is_MatMul = False¶
- is_Matrix = False¶
- is_Mul = False¶
- is_Not = False¶
- is_Number = False¶
- is_NumberSymbol = False¶
- is_Order = False¶
- is_Piecewise = False¶
- is_Point = False¶
- is_Poly = False¶
- is_Pow = False¶
- is_Rational = False¶
- is_Relational = False¶
- is_Symbol = True¶
- is_Vector = False¶
- is_Wild = False¶
- property is_algebraic¶
- is_algebraic_expr(*syms)¶
This tests whether a given expression is algebraic or not, in the given symbols, syms. When syms is not given, all free symbols will be used. The rational function does not have to be in expanded or in any kind of canonical form.
This function returns False for expressions that are “algebraic expressions” with symbolic exponents. This is a simple extension to the is_rational_function, including rational exponentiation.
See also
References
Examples
>>> from sympy import Symbol, sqrt >>> x = Symbol('x', real=True) >>> sqrt(1 + x).is_rational_function() False >>> sqrt(1 + x).is_algebraic_expr() True
This function does not attempt any nontrivial simplifications that may result in an expression that does not appear to be an algebraic expression to become one.
>>> from sympy import exp, factor >>> a = sqrt(exp(x)**2 + 2*exp(x) + 1)/(exp(x) + 1) >>> a.is_algebraic_expr(x) False >>> factor(a).is_algebraic_expr() True
- property is_antihermitian¶
- property is_commutative¶
- is_comparable = False¶
- property is_complex¶
- property is_composite¶
- is_constant(*wrt, **flags)¶
Return True if self is constant, False if not, or None if the constancy could not be determined conclusively.
Examples
>>> from sympy import cos, sin, Sum, S, pi >>> from sympy.abc import a, n, x, y >>> x.is_constant() False >>> S(2).is_constant() True >>> Sum(x, (x, 1, 10)).is_constant() True >>> Sum(x, (x, 1, n)).is_constant() False >>> Sum(x, (x, 1, n)).is_constant(y) True >>> Sum(x, (x, 1, n)).is_constant(n) False >>> Sum(x, (x, 1, n)).is_constant(x) True >>> eq = a*cos(x)**2 + a*sin(x)**2 - a >>> eq.is_constant() True >>> eq.subs({x: pi, a: 2}) == eq.subs({x: pi, a: 3}) == 0 True
>>> (0**x).is_constant() False >>> x.is_constant() False >>> (x**x).is_constant() False >>> one = cos(x)**2 + sin(x)**2 >>> one.is_constant() True >>> ((one - 1)**(x + 1)).is_constant() in (True, False) # could be 0 or 1 True
- property is_even¶
- property is_extended_negative¶
- property is_extended_nonnegative¶
- property is_extended_nonpositive¶
- property is_extended_nonzero¶
- property is_extended_positive¶
- property is_extended_real¶
- property is_finite¶
- property is_hermitian¶
- is_hypergeometric(k)¶
- property is_imaginary¶
- property is_infinite¶
- property is_integer¶
- property is_irrational¶
- is_meromorphic(x, a)¶
This tests whether an expression is meromorphic as a function of the given symbol
xat the pointa.This method is intended as a quick test that will return None if no decision can be made without simplification or more detailed analysis.
Examples
>>> from sympy import zoo, log, sin, sqrt >>> from sympy.abc import x
>>> f = 1/x**2 + 1 - 2*x**3 >>> f.is_meromorphic(x, 0) True >>> f.is_meromorphic(x, 1) True >>> f.is_meromorphic(x, zoo) True
>>> g = x**log(3) >>> g.is_meromorphic(x, 0) False >>> g.is_meromorphic(x, 1) True >>> g.is_meromorphic(x, zoo) False
>>> h = sin(1/x)*x**2 >>> h.is_meromorphic(x, 0) False >>> h.is_meromorphic(x, 1) True >>> h.is_meromorphic(x, zoo) True
Multivalued functions are considered meromorphic when their branches are meromorphic. Thus most functions are meromorphic everywhere except at essential singularities and branch points. In particular, they will be meromorphic also on branch cuts except at their endpoints.
>>> log(x).is_meromorphic(x, -1) True >>> log(x).is_meromorphic(x, 0) False >>> sqrt(x).is_meromorphic(x, -1) True >>> sqrt(x).is_meromorphic(x, 0) False
- property is_negative¶
- property is_noninteger¶
- property is_nonnegative¶
- property is_nonpositive¶
- property is_nonzero¶
- is_number = False¶
- property is_odd¶
- property is_polar¶
- is_polynomial(*syms)¶
Return True if self is a polynomial in syms and False otherwise.
This checks if self is an exact polynomial in syms. This function returns False for expressions that are “polynomials” with symbolic exponents. Thus, you should be able to apply polynomial algorithms to expressions for which this returns True, and Poly(expr, *syms) should work if and only if expr.is_polynomial(*syms) returns True. The polynomial does not have to be in expanded form. If no symbols are given, all free symbols in the expression will be used.
This is not part of the assumptions system. You cannot do Symbol(‘z’, polynomial=True).
Examples
>>> from sympy import Symbol, Function >>> x = Symbol('x') >>> ((x**2 + 1)**4).is_polynomial(x) True >>> ((x**2 + 1)**4).is_polynomial() True >>> (2**x + 1).is_polynomial(x) False >>> (2**x + 1).is_polynomial(2**x) True >>> f = Function('f') >>> (f(x) + 1).is_polynomial(x) False >>> (f(x) + 1).is_polynomial(f(x)) True >>> (1/f(x) + 1).is_polynomial(f(x)) False
>>> n = Symbol('n', nonnegative=True, integer=True) >>> (x**n + 1).is_polynomial(x) False
This function does not attempt any nontrivial simplifications that may result in an expression that does not appear to be a polynomial to become one.
>>> from sympy import sqrt, factor, cancel >>> y = Symbol('y', positive=True) >>> a = sqrt(y**2 + 2*y + 1) >>> a.is_polynomial(y) False >>> factor(a) y + 1 >>> factor(a).is_polynomial(y) True
>>> b = (y**2 + 2*y + 1)/(y + 1) >>> b.is_polynomial(y) False >>> cancel(b) y + 1 >>> cancel(b).is_polynomial(y) True
See also .is_rational_function()
- property is_positive¶
- property is_prime¶
- property is_rational¶
- is_rational_function(*syms)¶
Test whether function is a ratio of two polynomials in the given symbols, syms. When syms is not given, all free symbols will be used. The rational function does not have to be in expanded or in any kind of canonical form.
This function returns False for expressions that are “rational functions” with symbolic exponents. Thus, you should be able to call .as_numer_denom() and apply polynomial algorithms to the result for expressions for which this returns True.
This is not part of the assumptions system. You cannot do Symbol(‘z’, rational_function=True).
Examples
>>> from sympy import Symbol, sin >>> from sympy.abc import x, y
>>> (x/y).is_rational_function() True
>>> (x**2).is_rational_function() True
>>> (x/sin(y)).is_rational_function(y) False
>>> n = Symbol('n', integer=True) >>> (x**n + 1).is_rational_function(x) False
This function does not attempt any nontrivial simplifications that may result in an expression that does not appear to be a rational function to become one.
>>> from sympy import sqrt, factor >>> y = Symbol('y', positive=True) >>> a = sqrt(y**2 + 2*y + 1)/y >>> a.is_rational_function(y) False >>> factor(a) (y + 1)/y >>> factor(a).is_rational_function(y) True
See also is_algebraic_expr().
- property is_real¶
- is_scalar = True¶
- is_symbol = True¶
- property is_transcendental¶
- property is_zero¶
- property kind¶
Default kind for all SymPy object. If the kind is not defined for the object, or if the object cannot infer the kind from its arguments, this will be returned.
Examples
>>> from sympy import Expr >>> Expr().kind UndefinedKind
- leadterm(x, logx=None, cdir=0)¶
Returns the leading term a*x**b as a tuple (a, b).
Examples
>>> from sympy.abc import x >>> (1+x+x**2).leadterm(x) (1, 0) >>> (1/x**2+x+x**2).leadterm(x) (1, -2)
- limit(x, xlim, dir='+')¶
Compute limit x->xlim.
- lseries(x=None, x0=0, dir='+', logx=None, cdir=0)¶
Wrapper for series yielding an iterator of the terms of the series.
Note: an infinite series will yield an infinite iterator. The following, for exaxmple, will never terminate. It will just keep printing terms of the sin(x) series:
for term in sin(x).lseries(x): print term
The advantage of lseries() over nseries() is that many times you are just interested in the next term in the series (i.e. the first term for example), but you do not know how many you should ask for in nseries() using the “n” parameter.
See also nseries().
- match(pattern, old=False)¶
Pattern matching.
Wild symbols match all.
Return
Nonewhen expression (self) does not match with pattern. Otherwise return a dictionary such that:pattern.xreplace(self.match(pattern)) == self
Examples
>>> from sympy import Wild, Sum >>> from sympy.abc import x, y >>> p = Wild("p") >>> q = Wild("q") >>> r = Wild("r") >>> e = (x+y)**(x+y) >>> e.match(p**p) {p_: x + y} >>> e.match(p**q) {p_: x + y, q_: x + y} >>> e = (2*x)**2 >>> e.match(p*q**r) {p_: 4, q_: x, r_: 2} >>> (p*q**r).xreplace(e.match(p*q**r)) 4*x**2
Structurally bound symbols are ignored during matching:
>>> Sum(x, (x, 1, 2)).match(Sum(y, (y, 1, p))) {p_: 2}
But they can be identified if desired:
>>> Sum(x, (x, 1, 2)).match(Sum(q, (q, 1, p))) {p_: 2, q_: x}
The
oldflag will give the old-style pattern matching where expressions and patterns are essentially solved to give the match. Both of the following give None unlessold=True:>>> (x - 2).match(p - x, old=True) {p_: 2*x - 2} >>> (2/x).match(p*x, old=True) {p_: 2/x**2}
- matches(expr, repl_dict=None, old=False)¶
Helper method for match() that looks for a match between Wild symbols in self and expressions in expr.
Examples
>>> from sympy import symbols, Wild, Basic >>> a, b, c = symbols('a b c') >>> x = Wild('x') >>> Basic(a + x, x).matches(Basic(a + b, c)) is None True >>> Basic(a + x, x).matches(Basic(a + b + c, b + c)) {x_: b + c}
- n(n=15, subs=None, maxn=100, chop=False, strict=False, quad=None, verbose=False)¶
Evaluate the given formula to an accuracy of n digits.
- Parameters:
- subsdict, optional
Substitute numerical values for symbols, e.g.
subs={x:3, y:1+pi}. The substitutions must be given as a dictionary.- maxnint, optional
Allow a maximum temporary working precision of maxn digits.
- chopbool or number, optional
Specifies how to replace tiny real or imaginary parts in subresults by exact zeros.
When
Truethe chop value defaults to standard precision.Otherwise the chop value is used to determine the magnitude of “small” for purposes of chopping.
>>> from sympy import N >>> x = 1e-4 >>> N(x, chop=True) 0.000100000000000000 >>> N(x, chop=1e-5) 0.000100000000000000 >>> N(x, chop=1e-4) 0
- strictbool, optional
Raise
PrecisionExhaustedif any subresult fails to evaluate to full accuracy, given the available maxprec.- quadstr, optional
Choose algorithm for numerical quadrature. By default, tanh-sinh quadrature is used. For oscillatory integrals on an infinite interval, try
quad='osc'.- verbosebool, optional
Print debug information.
Notes
When Floats are naively substituted into an expression, precision errors may adversely affect the result. For example, adding 1e16 (a Float) to 1 will truncate to 1e16; if 1e16 is then subtracted, the result will be 0. That is exactly what happens in the following:
>>> from sympy.abc import x, y, z >>> values = {x: 1e16, y: 1, z: 1e16} >>> (x + y - z).subs(values) 0
Using the subs argument for evalf is the accurate way to evaluate such an expression:
>>> (x + y - z).evalf(subs=values) 1.00000000000000
- name: str¶
- normal()¶
Return the expression as a fraction.
expression -> a/b
See also
as_numer_denomreturn
(a, b)instead ofa/b
- nseries(x=None, x0=0, n=6, dir='+', logx=None, cdir=0)¶
Wrapper to _eval_nseries if assumptions allow, else to series.
If x is given, x0 is 0, dir=’+’, and self has x, then _eval_nseries is called. This calculates “n” terms in the innermost expressions and then builds up the final series just by “cross-multiplying” everything out.
The optional
logxparameter can be used to replace any log(x) in the returned series with a symbolic value to avoid evaluating log(x) at 0. A symbol to use in place of log(x) should be provided.Advantage – it’s fast, because we do not have to determine how many terms we need to calculate in advance.
Disadvantage – you may end up with less terms than you may have expected, but the O(x**n) term appended will always be correct and so the result, though perhaps shorter, will also be correct.
If any of those assumptions is not met, this is treated like a wrapper to series which will try harder to return the correct number of terms.
See also lseries().
Examples
>>> from sympy import sin, log, Symbol >>> from sympy.abc import x, y >>> sin(x).nseries(x, 0, 6) x - x**3/6 + x**5/120 + O(x**6) >>> log(x+1).nseries(x, 0, 5) x - x**2/2 + x**3/3 - x**4/4 + O(x**5)
Handling of the
logxparameter — in the following example the expansion fails sincesindoes not have an asymptotic expansion at -oo (the limit of log(x) as x approaches 0):>>> e = sin(log(x)) >>> e.nseries(x, 0, 6) Traceback (most recent call last): ... PoleError: ... ... >>> logx = Symbol('logx') >>> e.nseries(x, 0, 6, logx=logx) sin(logx)
In the following example, the expansion works but only returns self unless the
logxparameter is used:>>> e = x**y >>> e.nseries(x, 0, 2) x**y >>> e.nseries(x, 0, 2, logx=logx) exp(logx*y)
- nsimplify(constants=(), tolerance=None, full=False)¶
See the nsimplify function in sympy.simplify
- powsimp(*args, **kwargs)¶
See the powsimp function in sympy.simplify
- primitive()¶
Return the positive Rational that can be extracted non-recursively from every term of self (i.e., self is treated like an Add). This is like the as_coeff_Mul() method but primitive always extracts a positive Rational (never a negative or a Float).
Examples
>>> from sympy.abc import x >>> (3*(x + 1)**2).primitive() (3, (x + 1)**2) >>> a = (6*x + 2); a.primitive() (2, 3*x + 1) >>> b = (x/2 + 3); b.primitive() (1/2, x + 6) >>> (a*b).primitive() == (1, a*b) True
- radsimp(**kwargs)¶
See the radsimp function in sympy.simplify
- ratsimp()¶
See the ratsimp function in sympy.simplify
- rcall(*args)¶
Apply on the argument recursively through the expression tree.
This method is used to simulate a common abuse of notation for operators. For instance, in SymPy the following will not work:
(x+Lambda(y, 2*y))(z) == x+2*z,however, you can use:
>>> from sympy import Lambda >>> from sympy.abc import x, y, z >>> (x + Lambda(y, 2*y)).rcall(z) x + 2*z
- refine(assumption=True)¶
See the refine function in sympy.assumptions
- removeO()¶
Removes the additive O(..) symbol if there is one
- replace(query, value, map=False, simultaneous=True, exact=None)¶
Replace matching subexpressions of
selfwithvalue.If
map = Truethen also return the mapping {old: new} whereoldwas a sub-expression found with query andnewis the replacement value for it. If the expression itself does not match the query, then the returned value will beself.xreplace(map)otherwise it should beself.subs(ordered(map.items())).Traverses an expression tree and performs replacement of matching subexpressions from the bottom to the top of the tree. The default approach is to do the replacement in a simultaneous fashion so changes made are targeted only once. If this is not desired or causes problems,
simultaneouscan be set to False.In addition, if an expression containing more than one Wild symbol is being used to match subexpressions and the
exactflag is None it will be set to True so the match will only succeed if all non-zero values are received for each Wild that appears in the match pattern. Setting this to False accepts a match of 0; while setting it True accepts all matches that have a 0 in them. See example below for cautions.The list of possible combinations of queries and replacement values is listed below:
See also
Examples
Initial setup
>>> from sympy import log, sin, cos, tan, Wild, Mul, Add >>> from sympy.abc import x, y >>> f = log(sin(x)) + tan(sin(x**2))
- 1.1. type -> type
obj.replace(type, newtype)
When object of type
typeis found, replace it with the result of passing its argument(s) tonewtype.>>> f.replace(sin, cos) log(cos(x)) + tan(cos(x**2)) >>> sin(x).replace(sin, cos, map=True) (cos(x), {sin(x): cos(x)}) >>> (x*y).replace(Mul, Add) x + y
- 1.2. type -> func
obj.replace(type, func)
When object of type
typeis found, applyfuncto its argument(s).funcmust be written to handle the number of arguments oftype.>>> f.replace(sin, lambda arg: sin(2*arg)) log(sin(2*x)) + tan(sin(2*x**2)) >>> (x*y).replace(Mul, lambda *args: sin(2*Mul(*args))) sin(2*x*y)
- 2.1. pattern -> expr
obj.replace(pattern(wild), expr(wild))
Replace subexpressions matching
patternwith the expression written in terms of the Wild symbols inpattern.>>> a, b = map(Wild, 'ab') >>> f.replace(sin(a), tan(a)) log(tan(x)) + tan(tan(x**2)) >>> f.replace(sin(a), tan(a/2)) log(tan(x/2)) + tan(tan(x**2/2)) >>> f.replace(sin(a), a) log(x) + tan(x**2) >>> (x*y).replace(a*x, a) y
Matching is exact by default when more than one Wild symbol is used: matching fails unless the match gives non-zero values for all Wild symbols:
>>> (2*x + y).replace(a*x + b, b - a) y - 2 >>> (2*x).replace(a*x + b, b - a) 2*x
When set to False, the results may be non-intuitive:
>>> (2*x).replace(a*x + b, b - a, exact=False) 2/x
- 2.2. pattern -> func
obj.replace(pattern(wild), lambda wild: expr(wild))
All behavior is the same as in 2.1 but now a function in terms of pattern variables is used rather than an expression:
>>> f.replace(sin(a), lambda a: sin(2*a)) log(sin(2*x)) + tan(sin(2*x**2))
- 3.1. func -> func
obj.replace(filter, func)
Replace subexpression
ewithfunc(e)iffilter(e)is True.>>> g = 2*sin(x**3) >>> g.replace(lambda expr: expr.is_Number, lambda expr: expr**2) 4*sin(x**9)
The expression itself is also targeted by the query but is done in such a fashion that changes are not made twice.
>>> e = x*(x*y + 1) >>> e.replace(lambda x: x.is_Mul, lambda x: 2*x) 2*x*(2*x*y + 1)
When matching a single symbol, exact will default to True, but this may or may not be the behavior that is desired:
Here, we want exact=False:
>>> from sympy import Function >>> f = Function('f') >>> e = f(1) + f(0) >>> q = f(a), lambda a: f(a + 1) >>> e.replace(*q, exact=False) f(1) + f(2) >>> e.replace(*q, exact=True) f(0) + f(2)
But here, the nature of matching makes selecting the right setting tricky:
>>> e = x**(1 + y) >>> (x**(1 + y)).replace(x**(1 + a), lambda a: x**-a, exact=False) x >>> (x**(1 + y)).replace(x**(1 + a), lambda a: x**-a, exact=True) x**(-x - y + 1) >>> (x**y).replace(x**(1 + a), lambda a: x**-a, exact=False) x >>> (x**y).replace(x**(1 + a), lambda a: x**-a, exact=True) x**(1 - y)
It is probably better to use a different form of the query that describes the target expression more precisely:
>>> (1 + x**(1 + y)).replace( ... lambda x: x.is_Pow and x.exp.is_Add and x.exp.args[0] == 1, ... lambda x: x.base**(1 - (x.exp - 1))) ... x**(1 - y) + 1
- rewrite(*args, deep=True, **hints)¶
Rewrite self using a defined rule.
Rewriting transforms an expression to another, which is mathematically equivalent but structurally different. For example you can rewrite trigonometric functions as complex exponentials or combinatorial functions as gamma function.
This method takes a pattern and a rule as positional arguments. pattern is optional parameter which defines the types of expressions that will be transformed. If it is not passed, all possible expressions will be rewritten. rule defines how the expression will be rewritten.
- Parameters:
- argsExpr
A rule, or pattern and rule. - pattern is a type or an iterable of types. - rule can be any object.
- deepbool, optional
If
True, subexpressions are recursively transformed. Default isTrue.
Examples
If pattern is unspecified, all possible expressions are transformed.
>>> from sympy import cos, sin, exp, I >>> from sympy.abc import x >>> expr = cos(x) + I*sin(x) >>> expr.rewrite(exp) exp(I*x)
Pattern can be a type or an iterable of types.
>>> expr.rewrite(sin, exp) exp(I*x)/2 + cos(x) - exp(-I*x)/2 >>> expr.rewrite([cos,], exp) exp(I*x)/2 + I*sin(x) + exp(-I*x)/2 >>> expr.rewrite([cos, sin], exp) exp(I*x)
Rewriting behavior can be implemented by defining
_eval_rewrite()method.>>> from sympy import Expr, sqrt, pi >>> class MySin(Expr): ... def _eval_rewrite(self, rule, args, **hints): ... x, = args ... if rule == cos: ... return cos(pi/2 - x, evaluate=False) ... if rule == sqrt: ... return sqrt(1 - cos(x)**2) >>> MySin(MySin(x)).rewrite(cos) cos(-cos(-x + pi/2) + pi/2) >>> MySin(x).rewrite(sqrt) sqrt(1 - cos(x)**2)
Defining
_eval_rewrite_as_[...]()method is supported for backwards compatibility reason. This may be removed in the future and using it is discouraged.>>> class MySin(Expr): ... def _eval_rewrite_as_cos(self, *args, **hints): ... x, = args ... return cos(pi/2 - x, evaluate=False) >>> MySin(x).rewrite(cos) cos(-x + pi/2)
- round(n=None)¶
Return x rounded to the given decimal place.
If a complex number would results, apply round to the real and imaginary components of the number.
Notes
The Python
roundfunction uses the SymPyroundmethod so it will always return a SymPy number (not a Python float or int):>>> isinstance(round(S(123), -2), Number) True
Examples
>>> from sympy import pi, E, I, S, Number >>> pi.round() 3 >>> pi.round(2) 3.14 >>> (2*pi + E*I).round() 6 + 3*I
The round method has a chopping effect:
>>> (2*pi + I/10).round() 6 >>> (pi/10 + 2*I).round() 2*I >>> (pi/10 + E*I).round(2) 0.31 + 2.72*I
- separate(deep=False, force=False)¶
See the separate function in sympy.simplify
- series(x=None, x0=0, n=6, dir='+', logx=None, cdir=0)¶
Series expansion of “self” around
x = x0yielding either terms of the series one by one (the lazy series given when n=None), else all the terms at once when n != None.Returns the series expansion of “self” around the point
x = x0with respect toxup toO((x - x0)**n, x, x0)(default n is 6).If
x=Noneandselfis univariate, the univariate symbol will be supplied, otherwise an error will be raised.- Parameters:
- exprExpression
The expression whose series is to be expanded.
- xSymbol
It is the variable of the expression to be calculated.
- x0Value
The value around which
xis calculated. Can be any value from-ootooo.- nValue
The value used to represent the order in terms of
x**n, up to which the series is to be expanded.- dirString, optional
The series-expansion can be bi-directional. If
dir="+", then (x->x0+). Ifdir="-", then (x->x0-). For infinite ``x0(ooor-oo), thedirargument is determined from the direction of the infinity (i.e.,dir="-"foroo).- logxoptional
It is used to replace any log(x) in the returned series with a symbolic value rather than evaluating the actual value.
- cdiroptional
It stands for complex direction, and indicates the direction from which the expansion needs to be evaluated.
- Returns:
- ExprExpression
Series expansion of the expression about x0
- Raises:
- TypeError
If “n” and “x0” are infinity objects
- PoleError
If “x0” is an infinity object
Examples
>>> from sympy import cos, exp, tan >>> from sympy.abc import x, y >>> cos(x).series() 1 - x**2/2 + x**4/24 + O(x**6) >>> cos(x).series(n=4) 1 - x**2/2 + O(x**4) >>> cos(x).series(x, x0=1, n=2) cos(1) - (x - 1)*sin(1) + O((x - 1)**2, (x, 1)) >>> e = cos(x + exp(y)) >>> e.series(y, n=2) cos(x + 1) - y*sin(x + 1) + O(y**2) >>> e.series(x, n=2) cos(exp(y)) - x*sin(exp(y)) + O(x**2)
If
n=Nonethen a generator of the series terms will be returned.>>> term=cos(x).series(n=None) >>> [next(term) for i in range(2)] [1, -x**2/2]
For
dir=+(default) the series is calculated from the right and fordir=-the series from the left. For smooth functions this flag will not alter the results.>>> abs(x).series(dir="+") x >>> abs(x).series(dir="-") -x >>> f = tan(x) >>> f.series(x, 2, 6, "+") tan(2) + (1 + tan(2)**2)*(x - 2) + (x - 2)**2*(tan(2)**3 + tan(2)) + (x - 2)**3*(1/3 + 4*tan(2)**2/3 + tan(2)**4) + (x - 2)**4*(tan(2)**5 + 5*tan(2)**3/3 + 2*tan(2)/3) + (x - 2)**5*(2/15 + 17*tan(2)**2/15 + 2*tan(2)**4 + tan(2)**6) + O((x - 2)**6, (x, 2))
>>> f.series(x, 2, 3, "-") tan(2) + (2 - x)*(-tan(2)**2 - 1) + (2 - x)**2*(tan(2)**3 + tan(2)) + O((x - 2)**3, (x, 2))
For rational expressions this method may return original expression without the Order term. >>> (1/x).series(x, n=8) 1/x
- simplify(**kwargs)¶
See the simplify function in sympy.simplify
- sort_key(order=None)¶
Return a sort key.
Examples
>>> from sympy import S, I
>>> sorted([S(1)/2, I, -I], key=lambda x: x.sort_key()) [1/2, -I, I]
>>> S("[x, 1/x, 1/x**2, x**2, x**(1/2), x**(1/4), x**(3/2)]") [x, 1/x, x**(-2), x**2, sqrt(x), x**(1/4), x**(3/2)] >>> sorted(_, key=lambda x: x.sort_key()) [x**(-2), 1/x, x**(1/4), sqrt(x), x, x**(3/2), x**2]
- subs(*args, **kwargs)¶
Substitutes old for new in an expression after sympifying args.
- args is either:
two arguments, e.g. foo.subs(old, new)
- one iterable argument, e.g. foo.subs(iterable). The iterable may be
- o an iterable container with (old, new) pairs. In this case the
replacements are processed in the order given with successive patterns possibly affecting replacements already made.
- o a dict or set whose key/value items correspond to old/new pairs.
In this case the old/new pairs will be sorted by op count and in case of a tie, by number of args and the default_sort_key. The resulting sorted list is then processed as an iterable container (see previous).
If the keyword
simultaneousis True, the subexpressions will not be evaluated until all the substitutions have been made.See also
Examples
>>> from sympy import pi, exp, limit, oo >>> from sympy.abc import x, y >>> (1 + x*y).subs(x, pi) pi*y + 1 >>> (1 + x*y).subs({x:pi, y:2}) 1 + 2*pi >>> (1 + x*y).subs([(x, pi), (y, 2)]) 1 + 2*pi >>> reps = [(y, x**2), (x, 2)] >>> (x + y).subs(reps) 6 >>> (x + y).subs(reversed(reps)) x**2 + 2
>>> (x**2 + x**4).subs(x**2, y) y**2 + y
To replace only the x**2 but not the x**4, use xreplace:
>>> (x**2 + x**4).xreplace({x**2: y}) x**4 + y
To delay evaluation until all substitutions have been made, set the keyword
simultaneousto True:>>> (x/y).subs([(x, 0), (y, 0)]) 0 >>> (x/y).subs([(x, 0), (y, 0)], simultaneous=True) nan
This has the added feature of not allowing subsequent substitutions to affect those already made:
>>> ((x + y)/y).subs({x + y: y, y: x + y}) 1 >>> ((x + y)/y).subs({x + y: y, y: x + y}, simultaneous=True) y/(x + y)
In order to obtain a canonical result, unordered iterables are sorted by count_op length, number of arguments and by the default_sort_key to break any ties. All other iterables are left unsorted.
>>> from sympy import sqrt, sin, cos >>> from sympy.abc import a, b, c, d, e
>>> A = (sqrt(sin(2*x)), a) >>> B = (sin(2*x), b) >>> C = (cos(2*x), c) >>> D = (x, d) >>> E = (exp(x), e)
>>> expr = sqrt(sin(2*x))*sin(exp(x)*x)*cos(2*x) + sin(2*x)
>>> expr.subs(dict([A, B, C, D, E])) a*c*sin(d*e) + b
The resulting expression represents a literal replacement of the old arguments with the new arguments. This may not reflect the limiting behavior of the expression:
>>> (x**3 - 3*x).subs({x: oo}) nan
>>> limit(x**3 - 3*x, x, oo) oo
If the substitution will be followed by numerical evaluation, it is better to pass the substitution to evalf as
>>> (1/x).evalf(subs={x: 3.0}, n=21) 0.333333333333333333333
rather than
>>> (1/x).subs({x: 3.0}).evalf(21) 0.333333333333333314830
as the former will ensure that the desired level of precision is obtained.
- taylor_term(n, x, *previous_terms)¶
General method for the taylor term.
This method is slow, because it differentiates n-times. Subclasses can redefine it to make it faster by using the “previous_terms”.
- to_nnf(simplify=True)¶
- together(*args, **kwargs)¶
See the together function in sympy.polys
- transpose()¶
- trigsimp(**args)¶
See the trigsimp function in sympy.simplify
- xreplace(rule, hack2=False)¶
Replace occurrences of objects within the expression.
- Parameters:
- ruledict-like
Expresses a replacement rule
- Returns:
- xreplacethe result of the replacement
See also
Examples
>>> from sympy import symbols, pi, exp >>> x, y, z = symbols('x y z') >>> (1 + x*y).xreplace({x: pi}) pi*y + 1 >>> (1 + x*y).xreplace({x: pi, y: 2}) 1 + 2*pi
Replacements occur only if an entire node in the expression tree is matched:
>>> (x*y + z).xreplace({x*y: pi}) z + pi >>> (x*y*z).xreplace({x*y: pi}) x*y*z >>> (2*x).xreplace({2*x: y, x: z}) y >>> (2*2*x).xreplace({2*x: y, x: z}) 4*z >>> (x + y + 2).xreplace({x + y: 2}) x + y + 2 >>> (x + 2 + exp(x + 2)).xreplace({x + 2: y}) x + exp(y) + 2
xreplace does not differentiate between free and bound symbols. In the following, subs(x, y) would not change x since it is a bound symbol, but xreplace does:
>>> from sympy import Integral >>> Integral(x, (x, 1, 2*x)).xreplace({x: y}) Integral(y, (y, 1, 2*y))
Trying to replace x with an expression raises an error:
>>> Integral(x, (x, 1, 2*x)).xreplace({x: 2*y}) ValueError: Invalid limits given: ((2*y, 1, 4*y),)
Factor¶
- class nipy.algorithms.statistics.formula.formulae.Factor(name, levels, char='b')¶
Bases:
FormulaA qualitative variable in a regression model
A Factor is similar to R’s factor. The levels of the Factor can be either strings or ints.
- __init__(name, levels, char='b')¶
Initialize Factor
- Parameters:
- namestr
- levels[str or int]
A sequence of strings or ints.
- charstr, optional
prefix character for regression coefficients
- property coefs¶
Coefficients in the linear regression formula.
- design(input, param=None, return_float=False, contrasts=None)¶
Construct the design matrix, and optional contrast matrices.
- Parameters:
- inputnp.recarray
Recarray including fields needed to compute the Terms in getparams(self.design_expr).
- paramNone or np.recarray
Recarray including fields that are not Terms in getparams(self.design_expr)
- return_floatbool, optional
If True, return a np.float64 array rather than a np.recarray
- contrastsNone or dict, optional
Contrasts. The items in this dictionary should be (str, Formula) pairs where a contrast matrix is constructed for each Formula by evaluating its design at the same parameters as self.design. If not None, then the return_float is set to True.
- Returns:
- des2D array
design matrix
- cmatricesdict, optional
Dictionary with keys from contrasts input, and contrast matrices corresponding to des design matrix. Returned only if contrasts input is not None
- property design_expr¶
- property dtype¶
The dtype of the design matrix of the Formula.
- static fromcol(col, name)¶
Create a Factor from a column array.
- Parameters:
- colndarray
an array with ndim==1
- namestr
name of the Factor
- Returns:
- factorFactor
Examples
>>> data = np.array([(3,'a'),(4,'a'),(5,'b'),(3,'b')], np.dtype([('x', np.float64), ('y', 'S1')])) >>> f1 = Factor.fromcol(data['y'], 'y') >>> f2 = Factor.fromcol(data['x'], 'x') >>> d = f1.design(data) >>> print(d.dtype.descr) [('y_a', '<f8'), ('y_b', '<f8')] >>> d = f2.design(data) >>> print(d.dtype.descr) [('x_3', '<f8'), ('x_4', '<f8'), ('x_5', '<f8')]
- static fromrec(rec, keep=[], drop=[])¶
Construct Formula from recarray
For fields with a string-dtype, it is assumed that these are qualtiatitve regressors, i.e. Factors.
- Parameters:
- rec: recarray
Recarray whose field names will be used to create a formula.
- keep: []
Field names to explicitly keep, dropping all others.
- drop: []
Field names to drop.
- get_term(level)¶
Retrieve a term of the Factor…
- property main_effect¶
- property mean¶
Expression for the mean, expressed as a linear combination of terms, each with dummy variables in front.
- property params¶
The parameters in the Formula.
- stratify(variable)¶
Create a new variable, stratified by the levels of a Factor.
- Parameters:
- variablestr or simple sympy expression
If sympy expression, then string representation must be all lower or upper case letters, i.e. it can be interpreted as a name.
- Returns:
- formulaFormula
Formula whose mean has one parameter named variable%d, for each level in self.levels
Examples
>>> f = Factor('a', ['x','y']) >>> sf = f.stratify('theta') >>> sf.mean _theta0*a_x + _theta1*a_y
- subs(old, new)¶
Perform a sympy substitution on all terms in the Formula
Returns a new instance of the same class
- Parameters:
- oldsympy.Basic
The expression to be changed
- newsympy.Basic
The value to change it to.
- Returns:
- newfFormula
Examples
>>> s, t = [Term(l) for l in 'st'] >>> f, g = [sympy.Function(l) for l in 'fg'] >>> form = Formula([f(t),g(s)]) >>> newform = form.subs(g, sympy.Function('h')) >>> newform.terms array([f(t), h(s)], dtype=object) >>> form.terms array([f(t), g(s)], dtype=object)
- property terms¶
Terms in the linear regression formula.
FactorTerm¶
- class nipy.algorithms.statistics.formula.formulae.FactorTerm(name, level)¶
Bases:
TermBoolean Term derived from a Factor.
Its properties are the same as a Term except that its product with itself is itself.
- __init__(*args, **kwargs)¶
- adjoint()¶
- apart(x=None, **args)¶
See the apart function in sympy.polys
- property args: tuple[Basic, ...]¶
Returns a tuple of arguments of ‘self’.
Notes
Never use self._args, always use self.args. Only use _args in __new__ when creating a new function. Do not override .args() from Basic (so that it is easy to change the interface in the future if needed).
Examples
>>> from sympy import cot >>> from sympy.abc import x, y
>>> cot(x).args (x,)
>>> cot(x).args[0] x
>>> (x*y).args (x, y)
>>> (x*y).args[1] y
- args_cnc(cset=False, warn=True, split_1=True)¶
Return [commutative factors, non-commutative factors] of self.
Examples
>>> from sympy import symbols, oo >>> A, B = symbols('A B', commutative=0) >>> x, y = symbols('x y') >>> (-2*x*y).args_cnc() [[-1, 2, x, y], []] >>> (-2.5*x).args_cnc() [[-1, 2.5, x], []] >>> (-2*x*A*B*y).args_cnc() [[-1, 2, x, y], [A, B]] >>> (-2*x*A*B*y).args_cnc(split_1=False) [[-2, x, y], [A, B]] >>> (-2*x*y).args_cnc(cset=True) [{-1, 2, x, y}, []]
The arg is always treated as a Mul:
>>> (-2 + x + A).args_cnc() [[], [x - 2 + A]] >>> (-oo).args_cnc() # -oo is a singleton [[-1, oo], []]
- as_base_exp() tuple[Expr, Expr]¶
- as_coeff_Add(rational=False) tuple[Number, Expr]¶
Efficiently extract the coefficient of a summation.
- as_coeff_Mul(rational: bool = False) tuple[Number, Expr]¶
Efficiently extract the coefficient of a product.
- as_coeff_add(*deps) tuple[Expr, tuple[Expr, ...]]¶
Return the tuple (c, args) where self is written as an Add,
a.c should be a Rational added to any terms of the Add that are independent of deps.
args should be a tuple of all other terms of
a; args is empty if self is a Number or if self is independent of deps (when given).This should be used when you do not know if self is an Add or not but you want to treat self as an Add or if you want to process the individual arguments of the tail of self as an Add.
if you know self is an Add and want only the head, use self.args[0];
if you do not want to process the arguments of the tail but need the tail then use self.as_two_terms() which gives the head and tail.
if you want to split self into an independent and dependent parts use
self.as_independent(*deps)
>>> from sympy import S >>> from sympy.abc import x, y >>> (S(3)).as_coeff_add() (3, ()) >>> (3 + x).as_coeff_add() (3, (x,)) >>> (3 + x + y).as_coeff_add(x) (y + 3, (x,)) >>> (3 + y).as_coeff_add(x) (y + 3, ())
- as_coeff_exponent(x) tuple[Expr, Expr]¶
c*x**e -> c,ewhere x can be any symbolic expression.
- as_coeff_mul(*deps, **kwargs) tuple[Expr, tuple[Expr, ...]]¶
Return the tuple (c, args) where self is written as a Mul,
m.c should be a Rational multiplied by any factors of the Mul that are independent of deps.
args should be a tuple of all other factors of m; args is empty if self is a Number or if self is independent of deps (when given).
This should be used when you do not know if self is a Mul or not but you want to treat self as a Mul or if you want to process the individual arguments of the tail of self as a Mul.
if you know self is a Mul and want only the head, use self.args[0];
if you do not want to process the arguments of the tail but need the tail then use self.as_two_terms() which gives the head and tail;
if you want to split self into an independent and dependent parts use
self.as_independent(*deps)
>>> from sympy import S >>> from sympy.abc import x, y >>> (S(3)).as_coeff_mul() (3, ()) >>> (3*x*y).as_coeff_mul() (3, (x, y)) >>> (3*x*y).as_coeff_mul(x) (3*y, (x,)) >>> (3*y).as_coeff_mul(x) (3*y, ())
- as_coefficient(expr)¶
Extracts symbolic coefficient at the given expression. In other words, this functions separates ‘self’ into the product of ‘expr’ and ‘expr’-free coefficient. If such separation is not possible it will return None.
See also
coeffreturn sum of terms have a given factor
as_coeff_Addseparate the additive constant from an expression
as_coeff_Mulseparate the multiplicative constant from an expression
as_independentseparate x-dependent terms/factors from others
sympy.polys.polytools.Poly.coeff_monomialefficiently find the single coefficient of a monomial in Poly
sympy.polys.polytools.Poly.nthlike coeff_monomial but powers of monomial terms are used
Examples
>>> from sympy import E, pi, sin, I, Poly >>> from sympy.abc import x
>>> E.as_coefficient(E) 1 >>> (2*E).as_coefficient(E) 2 >>> (2*sin(E)*E).as_coefficient(E)
Two terms have E in them so a sum is returned. (If one were desiring the coefficient of the term exactly matching E then the constant from the returned expression could be selected. Or, for greater precision, a method of Poly can be used to indicate the desired term from which the coefficient is desired.)
>>> (2*E + x*E).as_coefficient(E) x + 2 >>> _.args[0] # just want the exact match 2 >>> p = Poly(2*E + x*E); p Poly(x*E + 2*E, x, E, domain='ZZ') >>> p.coeff_monomial(E) 2 >>> p.nth(0, 1) 2
Since the following cannot be written as a product containing E as a factor, None is returned. (If the coefficient
2*xis desired then thecoeffmethod should be used.)>>> (2*E*x + x).as_coefficient(E) >>> (2*E*x + x).coeff(E) 2*x
>>> (E*(x + 1) + x).as_coefficient(E)
>>> (2*pi*I).as_coefficient(pi*I) 2 >>> (2*I).as_coefficient(pi*I)
- as_coefficients_dict(*syms)¶
Return a dictionary mapping terms to their Rational coefficient. Since the dictionary is a defaultdict, inquiries about terms which were not present will return a coefficient of 0.
If symbols
symsare provided, any multiplicative terms independent of them will be considered a coefficient and a regular dictionary of syms-dependent generators as keys and their corresponding coefficients as values will be returned.Examples
>>> from sympy.abc import a, x, y >>> (3*x + a*x + 4).as_coefficients_dict() {1: 4, x: 3, a*x: 1} >>> _[a] 0 >>> (3*a*x).as_coefficients_dict() {a*x: 3} >>> (3*a*x).as_coefficients_dict(x) {x: 3*a} >>> (3*a*x).as_coefficients_dict(y) {1: 3*a*x}
- as_content_primitive(radical=False, clear=True)¶
This method should recursively remove a Rational from all arguments and return that (content) and the new self (primitive). The content should always be positive and
Mul(*foo.as_content_primitive()) == foo. The primitive need not be in canonical form and should try to preserve the underlying structure if possible (i.e. expand_mul should not be applied to self).Examples
>>> from sympy import sqrt >>> from sympy.abc import x, y, z
>>> eq = 2 + 2*x + 2*y*(3 + 3*y)
The as_content_primitive function is recursive and retains structure:
>>> eq.as_content_primitive() (2, x + 3*y*(y + 1) + 1)
Integer powers will have Rationals extracted from the base:
>>> ((2 + 6*x)**2).as_content_primitive() (4, (3*x + 1)**2) >>> ((2 + 6*x)**(2*y)).as_content_primitive() (1, (2*(3*x + 1))**(2*y))
Terms may end up joining once their as_content_primitives are added:
>>> ((5*(x*(1 + y)) + 2*x*(3 + 3*y))).as_content_primitive() (11, x*(y + 1)) >>> ((3*(x*(1 + y)) + 2*x*(3 + 3*y))).as_content_primitive() (9, x*(y + 1)) >>> ((3*(z*(1 + y)) + 2.0*x*(3 + 3*y))).as_content_primitive() (1, 6.0*x*(y + 1) + 3*z*(y + 1)) >>> ((5*(x*(1 + y)) + 2*x*(3 + 3*y))**2).as_content_primitive() (121, x**2*(y + 1)**2) >>> ((x*(1 + y) + 0.4*x*(3 + 3*y))**2).as_content_primitive() (1, 4.84*x**2*(y + 1)**2)
Radical content can also be factored out of the primitive:
>>> (2*sqrt(2) + 4*sqrt(10)).as_content_primitive(radical=True) (2, sqrt(2)*(1 + 2*sqrt(5)))
If clear=False (default is True) then content will not be removed from an Add if it can be distributed to leave one or more terms with integer coefficients.
>>> (x/2 + y).as_content_primitive() (1/2, x + 2*y) >>> (x/2 + y).as_content_primitive(clear=False) (1, x/2 + y)
- as_dummy()¶
Return the expression with any objects having structurally bound symbols replaced with unique, canonical symbols within the object in which they appear and having only the default assumption for commutativity being True. When applied to a symbol a new symbol having only the same commutativity will be returned.
Notes
Any object that has structurally bound variables should have a property, bound_symbols that returns those symbols appearing in the object.
Examples
>>> from sympy import Integral, Symbol >>> from sympy.abc import x >>> r = Symbol('r', real=True) >>> Integral(r, (r, x)).as_dummy() Integral(_0, (_0, x)) >>> _.variables[0].is_real is None True >>> r.as_dummy() _r
- as_expr(*gens)¶
Convert a polynomial to a SymPy expression.
Examples
>>> from sympy import sin >>> from sympy.abc import x, y
>>> f = (x**2 + x*y).as_poly(x, y) >>> f.as_expr() x**2 + x*y
>>> sin(x).as_expr() sin(x)
- as_independent(*deps, **hint) tuple[Expr, Expr]¶
A mostly naive separation of a Mul or Add into arguments that are not are dependent on deps. To obtain as complete a separation of variables as possible, use a separation method first, e.g.:
separatevars() to change Mul, Add and Pow (including exp) into Mul
.expand(mul=True) to change Add or Mul into Add
.expand(log=True) to change log expr into an Add
The only non-naive thing that is done here is to respect noncommutative ordering of variables and to always return (0, 0) for self of zero regardless of hints.
For nonzero self, the returned tuple (i, d) has the following interpretation:
i will has no variable that appears in deps
d will either have terms that contain variables that are in deps, or be equal to 0 (when self is an Add) or 1 (when self is a Mul)
if self is an Add then self = i + d
if self is a Mul then self = i*d
otherwise (self, S.One) or (S.One, self) is returned.
To force the expression to be treated as an Add, use the hint as_Add=True
See also
separatevarsexpand_logsympy.core.add.Add.as_two_termssympy.core.mul.Mul.as_two_termsas_coeff_mul
Examples
– self is an Add
>>> from sympy import sin, cos, exp >>> from sympy.abc import x, y, z
>>> (x + x*y).as_independent(x) (0, x*y + x) >>> (x + x*y).as_independent(y) (x, x*y) >>> (2*x*sin(x) + y + x + z).as_independent(x) (y + z, 2*x*sin(x) + x) >>> (2*x*sin(x) + y + x + z).as_independent(x, y) (z, 2*x*sin(x) + x + y)
– self is a Mul
>>> (x*sin(x)*cos(y)).as_independent(x) (cos(y), x*sin(x))
non-commutative terms cannot always be separated out when self is a Mul
>>> from sympy import symbols >>> n1, n2, n3 = symbols('n1 n2 n3', commutative=False) >>> (n1 + n1*n2).as_independent(n2) (n1, n1*n2) >>> (n2*n1 + n1*n2).as_independent(n2) (0, n1*n2 + n2*n1) >>> (n1*n2*n3).as_independent(n1) (1, n1*n2*n3) >>> (n1*n2*n3).as_independent(n2) (n1, n2*n3) >>> ((x-n1)*(x-y)).as_independent(x) (1, (x - y)*(x - n1))
– self is anything else:
>>> (sin(x)).as_independent(x) (1, sin(x)) >>> (sin(x)).as_independent(y) (sin(x), 1) >>> exp(x+y).as_independent(x) (1, exp(x + y))
– force self to be treated as an Add:
>>> (3*x).as_independent(x, as_Add=True) (0, 3*x)
– force self to be treated as a Mul:
>>> (3+x).as_independent(x, as_Add=False) (1, x + 3) >>> (-3+x).as_independent(x, as_Add=False) (1, x - 3)
Note how the below differs from the above in making the constant on the dep term positive.
>>> (y*(-3+x)).as_independent(x) (y, x - 3)
- – use .as_independent() for true independence testing instead
of .has(). The former considers only symbols in the free symbols while the latter considers all symbols
>>> from sympy import Integral >>> I = Integral(x, (x, 1, 2)) >>> I.has(x) True >>> x in I.free_symbols False >>> I.as_independent(x) == (I, 1) True >>> (I + x).as_independent(x) == (I, x) True
Note: when trying to get independent terms, a separation method might need to be used first. In this case, it is important to keep track of what you send to this routine so you know how to interpret the returned values
>>> from sympy import separatevars, log >>> separatevars(exp(x+y)).as_independent(x) (exp(y), exp(x)) >>> (x + x*y).as_independent(y) (x, x*y) >>> separatevars(x + x*y).as_independent(y) (x, y + 1) >>> (x*(1 + y)).as_independent(y) (x, y + 1) >>> (x*(1 + y)).expand(mul=True).as_independent(y) (x, x*y) >>> a, b=symbols('a b', positive=True) >>> (log(a*b).expand(log=True)).as_independent(b) (log(a), log(b))
- as_leading_term(*symbols, logx=None, cdir=0)¶
Returns the leading (nonzero) term of the series expansion of self.
The _eval_as_leading_term routines are used to do this, and they must always return a non-zero value.
Examples
>>> from sympy.abc import x >>> (1 + x + x**2).as_leading_term(x) 1 >>> (1/x**2 + x + x**2).as_leading_term(x) x**(-2)
- as_numer_denom()¶
Return the numerator and the denominator of an expression.
expression -> a/b -> a, b
This is just a stub that should be defined by an object’s class methods to get anything else.
See also
normalreturn
a/binstead of(a, b)
- as_ordered_factors(order=None)¶
Return list of ordered factors (if Mul) else [self].
- as_ordered_terms(order=None, data=False)¶
Transform an expression to an ordered list of terms.
Examples
>>> from sympy import sin, cos >>> from sympy.abc import x
>>> (sin(x)**2*cos(x) + sin(x)**2 + 1).as_ordered_terms() [sin(x)**2*cos(x), sin(x)**2, 1]
- as_poly(*gens, **args)¶
Converts
selfto a polynomial or returnsNone.
- as_powers_dict()¶
Return self as a dictionary of factors with each factor being treated as a power. The keys are the bases of the factors and the values, the corresponding exponents. The resulting dictionary should be used with caution if the expression is a Mul and contains non- commutative factors since the order that they appeared will be lost in the dictionary.
See also
as_ordered_factorsAn alternative for noncommutative applications, returning an ordered list of factors.
args_cncSimilar to as_ordered_factors, but guarantees separation of commutative and noncommutative factors.
- as_real_imag(deep=True, **hints)¶
Performs complex expansion on ‘self’ and returns a tuple containing collected both real and imaginary parts. This method cannot be confused with re() and im() functions, which does not perform complex expansion at evaluation.
However it is possible to expand both re() and im() functions and get exactly the same results as with a single call to this function.
>>> from sympy import symbols, I
>>> x, y = symbols('x,y', real=True)
>>> (x + y*I).as_real_imag() (x, y)
>>> from sympy.abc import z, w
>>> (z + w*I).as_real_imag() (re(z) - im(w), re(w) + im(z))
- as_set()¶
Rewrites Boolean expression in terms of real sets.
Examples
>>> from sympy import Symbol, Eq, Or, And >>> x = Symbol('x', real=True) >>> Eq(x, 0).as_set() {0} >>> (x > 0).as_set() Interval.open(0, oo) >>> And(-2 < x, x < 2).as_set() Interval.open(-2, 2) >>> Or(x < -2, 2 < x).as_set() Union(Interval.open(-oo, -2), Interval.open(2, oo))
- as_terms()¶
Transform an expression to a list of terms.
- aseries(x=None, n=6, bound=0, hir=False)¶
Asymptotic Series expansion of self. This is equivalent to
self.series(x, oo, n).- Parameters:
- selfExpression
The expression whose series is to be expanded.
- xSymbol
It is the variable of the expression to be calculated.
- nValue
The value used to represent the order in terms of
x**n, up to which the series is to be expanded.- hirBoolean
Set this parameter to be True to produce hierarchical series. It stops the recursion at an early level and may provide nicer and more useful results.
- boundValue, Integer
Use the
boundparameter to give limit on rewriting coefficients in its normalised form.
- Returns:
- Expr
Asymptotic series expansion of the expression.
See also
Expr.aseriesSee the docstring of this function for complete details of this wrapper.
Notes
This algorithm is directly induced from the limit computational algorithm provided by Gruntz. It majorly uses the mrv and rewrite sub-routines. The overall idea of this algorithm is first to look for the most rapidly varying subexpression w of a given expression f and then expands f in a series in w. Then same thing is recursively done on the leading coefficient till we get constant coefficients.
If the most rapidly varying subexpression of a given expression f is f itself, the algorithm tries to find a normalised representation of the mrv set and rewrites f using this normalised representation.
If the expansion contains an order term, it will be either
O(x ** (-n))orO(w ** (-n))wherewbelongs to the most rapidly varying expression ofself.References
[1]Gruntz, Dominik. A new algorithm for computing asymptotic series. In: Proc. 1993 Int. Symp. Symbolic and Algebraic Computation. 1993. pp. 239-244.
[2]Gruntz thesis - p90
Examples
>>> from sympy import sin, exp >>> from sympy.abc import x
>>> e = sin(1/x + exp(-x)) - sin(1/x)
>>> e.aseries(x) (1/(24*x**4) - 1/(2*x**2) + 1 + O(x**(-6), (x, oo)))*exp(-x)
>>> e.aseries(x, n=3, hir=True) -exp(-2*x)*sin(1/x)/2 + exp(-x)*cos(1/x) + O(exp(-3*x), (x, oo))
>>> e = exp(exp(x)/(1 - 1/x))
>>> e.aseries(x) exp(exp(x)/(1 - 1/x))
>>> e.aseries(x, bound=3) exp(exp(x)/x**2)*exp(exp(x)/x)*exp(-exp(x) + exp(x)/(1 - 1/x) - exp(x)/x - exp(x)/x**2)*exp(exp(x))
For rational expressions this method may return original expression without the Order term. >>> (1/x).aseries(x, n=8) 1/x
- property assumptions0¶
Return object type assumptions.
For example:
Symbol(‘x’, real=True) Symbol(‘x’, integer=True)
are different objects. In other words, besides Python type (Symbol in this case), the initial assumptions are also forming their typeinfo.
Examples
>>> from sympy import Symbol >>> from sympy.abc import x >>> x.assumptions0 {'commutative': True} >>> x = Symbol("x", positive=True) >>> x.assumptions0 {'commutative': True, 'complex': True, 'extended_negative': False, 'extended_nonnegative': True, 'extended_nonpositive': False, 'extended_nonzero': True, 'extended_positive': True, 'extended_real': True, 'finite': True, 'hermitian': True, 'imaginary': False, 'infinite': False, 'negative': False, 'nonnegative': True, 'nonpositive': False, 'nonzero': True, 'positive': True, 'real': True, 'zero': False}
- atoms(*types)¶
Returns the atoms that form the current object.
By default, only objects that are truly atomic and cannot be divided into smaller pieces are returned: symbols, numbers, and number symbols like I and pi. It is possible to request atoms of any type, however, as demonstrated below.
Examples
>>> from sympy import I, pi, sin >>> from sympy.abc import x, y >>> (1 + x + 2*sin(y + I*pi)).atoms() {1, 2, I, pi, x, y}
If one or more types are given, the results will contain only those types of atoms.
>>> from sympy import Number, NumberSymbol, Symbol >>> (1 + x + 2*sin(y + I*pi)).atoms(Symbol) {x, y}
>>> (1 + x + 2*sin(y + I*pi)).atoms(Number) {1, 2}
>>> (1 + x + 2*sin(y + I*pi)).atoms(Number, NumberSymbol) {1, 2, pi}
>>> (1 + x + 2*sin(y + I*pi)).atoms(Number, NumberSymbol, I) {1, 2, I, pi}
Note that I (imaginary unit) and zoo (complex infinity) are special types of number symbols and are not part of the NumberSymbol class.
The type can be given implicitly, too:
>>> (1 + x + 2*sin(y + I*pi)).atoms(x) # x is a Symbol {x, y}
Be careful to check your assumptions when using the implicit option since
S(1).is_Integer = Truebuttype(S(1))isOne, a special type of SymPy atom, whiletype(S(2))is typeIntegerand will find all integers in an expression:>>> from sympy import S >>> (1 + x + 2*sin(y + I*pi)).atoms(S(1)) {1}
>>> (1 + x + 2*sin(y + I*pi)).atoms(S(2)) {1, 2}
Finally, arguments to atoms() can select more than atomic atoms: any SymPy type (loaded in core/__init__.py) can be listed as an argument and those types of “atoms” as found in scanning the arguments of the expression recursively:
>>> from sympy import Function, Mul >>> from sympy.core.function import AppliedUndef >>> f = Function('f') >>> (1 + f(x) + 2*sin(y + I*pi)).atoms(Function) {f(x), sin(y + I*pi)} >>> (1 + f(x) + 2*sin(y + I*pi)).atoms(AppliedUndef) {f(x)}
>>> (1 + x + 2*sin(y + I*pi)).atoms(Mul) {I*pi, 2*sin(y + I*pi)}
- property binary_symbols¶
Return from the atoms of self those which are free symbols.
Not all free symbols are
Symbol. Eg: IndexedBase(‘I’)[0].free_symbolsFor most expressions, all symbols are free symbols. For some classes this is not true. e.g. Integrals use Symbols for the dummy variables which are bound variables, so Integral has a method to return all symbols except those. Derivative keeps track of symbols with respect to which it will perform a derivative; those are bound variables, too, so it has its own free_symbols method.
Any other method that uses bound variables should implement a free_symbols method.
- cancel(*gens, **args)¶
See the cancel function in sympy.polys
- property canonical_variables¶
Return a dictionary mapping any variable defined in
self.bound_symbolsto Symbols that do not clash with any free symbols in the expression.Examples
>>> from sympy import Lambda >>> from sympy.abc import x >>> Lambda(x, 2*x).canonical_variables {x: _0}
- classmethod class_key()¶
Nice order of classes.
- coeff(x, n=1, right=False, _first=True)¶
Returns the coefficient from the term(s) containing
x**n. Ifnis zero then all terms independent ofxwill be returned.See also
as_coefficientseparate the expression into a coefficient and factor
as_coeff_Addseparate the additive constant from an expression
as_coeff_Mulseparate the multiplicative constant from an expression
as_independentseparate x-dependent terms/factors from others
sympy.polys.polytools.Poly.coeff_monomialefficiently find the single coefficient of a monomial in Poly
sympy.polys.polytools.Poly.nthlike coeff_monomial but powers of monomial terms are used
Examples
>>> from sympy import symbols >>> from sympy.abc import x, y, z
You can select terms that have an explicit negative in front of them:
>>> (-x + 2*y).coeff(-1) x >>> (x - 2*y).coeff(-1) 2*y
You can select terms with no Rational coefficient:
>>> (x + 2*y).coeff(1) x >>> (3 + 2*x + 4*x**2).coeff(1) 0
You can select terms independent of x by making n=0; in this case expr.as_independent(x)[0] is returned (and 0 will be returned instead of None):
>>> (3 + 2*x + 4*x**2).coeff(x, 0) 3 >>> eq = ((x + 1)**3).expand() + 1 >>> eq x**3 + 3*x**2 + 3*x + 2 >>> [eq.coeff(x, i) for i in reversed(range(4))] [1, 3, 3, 2] >>> eq -= 2 >>> [eq.coeff(x, i) for i in reversed(range(4))] [1, 3, 3, 0]
You can select terms that have a numerical term in front of them:
>>> (-x - 2*y).coeff(2) -y >>> from sympy import sqrt >>> (x + sqrt(2)*x).coeff(sqrt(2)) x
The matching is exact:
>>> (3 + 2*x + 4*x**2).coeff(x) 2 >>> (3 + 2*x + 4*x**2).coeff(x**2) 4 >>> (3 + 2*x + 4*x**2).coeff(x**3) 0 >>> (z*(x + y)**2).coeff((x + y)**2) z >>> (z*(x + y)**2).coeff(x + y) 0
In addition, no factoring is done, so 1 + z*(1 + y) is not obtained from the following:
>>> (x + z*(x + x*y)).coeff(x) 1
If such factoring is desired, factor_terms can be used first:
>>> from sympy import factor_terms >>> factor_terms(x + z*(x + x*y)).coeff(x) z*(y + 1) + 1
>>> n, m, o = symbols('n m o', commutative=False) >>> n.coeff(n) 1 >>> (3*n).coeff(n) 3 >>> (n*m + m*n*m).coeff(n) # = (1 + m)*n*m 1 + m >>> (n*m + m*n*m).coeff(n, right=True) # = (1 + m)*n*m m
If there is more than one possible coefficient 0 is returned:
>>> (n*m + m*n).coeff(n) 0
If there is only one possible coefficient, it is returned:
>>> (n*m + x*m*n).coeff(m*n) x >>> (n*m + x*m*n).coeff(m*n, right=1) 1
- collect(syms, func=None, evaluate=True, exact=False, distribute_order_term=True)¶
See the collect function in sympy.simplify
- combsimp()¶
See the combsimp function in sympy.simplify
- compare(other)¶
Return -1, 0, 1 if the object is smaller, equal, or greater than other.
Not in the mathematical sense. If the object is of a different type from the “other” then their classes are ordered according to the sorted_classes list.
Examples
>>> from sympy.abc import x, y >>> x.compare(y) -1 >>> x.compare(x) 0 >>> y.compare(x) 1
- compute_leading_term(x, logx=None)¶
Deprecated function to compute the leading term of a series.
as_leading_term is only allowed for results of .series() This is a wrapper to compute a series first.
- conjugate()¶
Returns the complex conjugate of ‘self’.
- copy()¶
- could_extract_minus_sign()¶
Return True if self has -1 as a leading factor or has more literal negative signs than positive signs in a sum, otherwise False.
Examples
>>> from sympy.abc import x, y >>> e = x - y >>> {i.could_extract_minus_sign() for i in (e, -e)} {False, True}
Though the
y - xis considered like-(x - y), since it is in a product without a leading factor of -1, the result is false below:>>> (x*(y - x)).could_extract_minus_sign() False
To put something in canonical form wrt to sign, use signsimp:
>>> from sympy import signsimp >>> signsimp(x*(y - x)) -x*(x - y) >>> _.could_extract_minus_sign() True
- count(query)¶
Count the number of matching subexpressions.
- count_ops(visual=None)¶
Wrapper for count_ops that returns the operation count.
- default_assumptions = {}¶
- diff(*symbols, **assumptions)¶
- dir(x, cdir)¶
- doit(**hints)¶
Evaluate objects that are not evaluated by default like limits, integrals, sums and products. All objects of this kind will be evaluated recursively, unless some species were excluded via ‘hints’ or unless the ‘deep’ hint was set to ‘False’.
>>> from sympy import Integral >>> from sympy.abc import x
>>> 2*Integral(x, x) 2*Integral(x, x)
>>> (2*Integral(x, x)).doit() x**2
>>> (2*Integral(x, x)).doit(deep=False) 2*Integral(x, x)
- dummy_eq(other, symbol=None)¶
Compare two expressions and handle dummy symbols.
Examples
>>> from sympy import Dummy >>> from sympy.abc import x, y
>>> u = Dummy('u')
>>> (u**2 + 1).dummy_eq(x**2 + 1) True >>> (u**2 + 1) == (x**2 + 1) False
>>> (u**2 + y).dummy_eq(x**2 + y, x) True >>> (u**2 + y).dummy_eq(x**2 + y, y) False
- equals(other, failing_expression=False)¶
Return True if self == other, False if it does not, or None. If failing_expression is True then the expression which did not simplify to a 0 will be returned instead of None.
- evalf(n=15, subs=None, maxn=100, chop=False, strict=False, quad=None, verbose=False)¶
Evaluate the given formula to an accuracy of n digits.
- Parameters:
- subsdict, optional
Substitute numerical values for symbols, e.g.
subs={x:3, y:1+pi}. The substitutions must be given as a dictionary.- maxnint, optional
Allow a maximum temporary working precision of maxn digits.
- chopbool or number, optional
Specifies how to replace tiny real or imaginary parts in subresults by exact zeros.
When
Truethe chop value defaults to standard precision.Otherwise the chop value is used to determine the magnitude of “small” for purposes of chopping.
>>> from sympy import N >>> x = 1e-4 >>> N(x, chop=True) 0.000100000000000000 >>> N(x, chop=1e-5) 0.000100000000000000 >>> N(x, chop=1e-4) 0
- strictbool, optional
Raise
PrecisionExhaustedif any subresult fails to evaluate to full accuracy, given the available maxprec.- quadstr, optional
Choose algorithm for numerical quadrature. By default, tanh-sinh quadrature is used. For oscillatory integrals on an infinite interval, try
quad='osc'.- verbosebool, optional
Print debug information.
Notes
When Floats are naively substituted into an expression, precision errors may adversely affect the result. For example, adding 1e16 (a Float) to 1 will truncate to 1e16; if 1e16 is then subtracted, the result will be 0. That is exactly what happens in the following:
>>> from sympy.abc import x, y, z >>> values = {x: 1e16, y: 1, z: 1e16} >>> (x + y - z).subs(values) 0
Using the subs argument for evalf is the accurate way to evaluate such an expression:
>>> (x + y - z).evalf(subs=values) 1.00000000000000
- expand(deep=True, modulus=None, power_base=True, power_exp=True, mul=True, log=True, multinomial=True, basic=True, **hints)¶
Expand an expression using hints.
See the docstring of the expand() function in sympy.core.function for more information.
- property expr_free_symbols¶
Like
free_symbols, but returns the free symbols only if they are contained in an expression node.Examples
>>> from sympy.abc import x, y >>> (x + y).expr_free_symbols {x, y}
If the expression is contained in a non-expression object, do not return the free symbols. Compare:
>>> from sympy import Tuple >>> t = Tuple(x + y) >>> t.expr_free_symbols set() >>> t.free_symbols {x, y}
- extract_additively(c)¶
Return self - c if it’s possible to subtract c from self and make all matching coefficients move towards zero, else return None.
See also
Examples
>>> from sympy.abc import x, y >>> e = 2*x + 3 >>> e.extract_additively(x + 1) x + 2 >>> e.extract_additively(3*x) >>> e.extract_additively(4) >>> (y*(x + 1)).extract_additively(x + 1) >>> ((x + 1)*(x + 2*y + 1) + 3).extract_additively(x + 1) (x + 1)*(x + 2*y) + 3
- extract_branch_factor(allow_half=False)¶
Try to write self as
exp_polar(2*pi*I*n)*zin a nice way. Return (z, n).>>> from sympy import exp_polar, I, pi >>> from sympy.abc import x, y >>> exp_polar(I*pi).extract_branch_factor() (exp_polar(I*pi), 0) >>> exp_polar(2*I*pi).extract_branch_factor() (1, 1) >>> exp_polar(-pi*I).extract_branch_factor() (exp_polar(I*pi), -1) >>> exp_polar(3*pi*I + x).extract_branch_factor() (exp_polar(x + I*pi), 1) >>> (y*exp_polar(-5*pi*I)*exp_polar(3*pi*I + 2*pi*x)).extract_branch_factor() (y*exp_polar(2*pi*x), -1) >>> exp_polar(-I*pi/2).extract_branch_factor() (exp_polar(-I*pi/2), 0)
If allow_half is True, also extract exp_polar(I*pi):
>>> exp_polar(I*pi).extract_branch_factor(allow_half=True) (1, 1/2) >>> exp_polar(2*I*pi).extract_branch_factor(allow_half=True) (1, 1) >>> exp_polar(3*I*pi).extract_branch_factor(allow_half=True) (1, 3/2) >>> exp_polar(-I*pi).extract_branch_factor(allow_half=True) (1, -1/2)
- extract_multiplicatively(c)¶
Return None if it’s not possible to make self in the form c * something in a nice way, i.e. preserving the properties of arguments of self.
Examples
>>> from sympy import symbols, Rational
>>> x, y = symbols('x,y', real=True)
>>> ((x*y)**3).extract_multiplicatively(x**2 * y) x*y**2
>>> ((x*y)**3).extract_multiplicatively(x**4 * y)
>>> (2*x).extract_multiplicatively(2) x
>>> (2*x).extract_multiplicatively(3)
>>> (Rational(1, 2)*x).extract_multiplicatively(3) x/6
- factor(*gens, **args)¶
See the factor() function in sympy.polys.polytools
- find(query, group=False)¶
Find all subexpressions matching a query.
- property formula¶
Return a Formula with only terms=[self].
- fourier_series(limits=None)¶
Compute fourier sine/cosine series of self.
See the docstring of the
fourier_series()in sympy.series.fourier for more information.
- fps(x=None, x0=0, dir=1, hyper=True, order=4, rational=True, full=False)¶
Compute formal power power series of self.
See the docstring of the
fps()function in sympy.series.formal for more information.
- property free_symbols¶
Return from the atoms of self those which are free symbols.
Not all free symbols are
Symbol. Eg: IndexedBase(‘I’)[0].free_symbolsFor most expressions, all symbols are free symbols. For some classes this is not true. e.g. Integrals use Symbols for the dummy variables which are bound variables, so Integral has a method to return all symbols except those. Derivative keeps track of symbols with respect to which it will perform a derivative; those are bound variables, too, so it has its own free_symbols method.
Any other method that uses bound variables should implement a free_symbols method.
- classmethod fromiter(args, **assumptions)¶
Create a new object from an iterable.
This is a convenience function that allows one to create objects from any iterable, without having to convert to a list or tuple first.
Examples
>>> from sympy import Tuple >>> Tuple.fromiter(i for i in range(5)) (0, 1, 2, 3, 4)
- property func¶
The top-level function in an expression.
The following should hold for all objects:
>> x == x.func(*x.args)
Examples
>>> from sympy.abc import x >>> a = 2*x >>> a.func <class 'sympy.core.mul.Mul'> >>> a.args (2, x) >>> a.func(*a.args) 2*x >>> a == a.func(*a.args) True
- gammasimp()¶
See the gammasimp function in sympy.simplify
- getO()¶
Returns the additive O(..) symbol if there is one, else None.
- getn()¶
Returns the order of the expression.
Examples
>>> from sympy import O >>> from sympy.abc import x >>> (1 + x + O(x**2)).getn() 2 >>> (1 + x).getn()
- has(*patterns)¶
Test whether any subexpression matches any of the patterns.
Examples
>>> from sympy import sin >>> from sympy.abc import x, y, z >>> (x**2 + sin(x*y)).has(z) False >>> (x**2 + sin(x*y)).has(x, y, z) True >>> x.has(x) True
Note
hasis a structural algorithm with no knowledge of mathematics. Consider the following half-open interval:>>> from sympy import Interval >>> i = Interval.Lopen(0, 5); i Interval.Lopen(0, 5) >>> i.args (0, 5, True, False) >>> i.has(4) # there is no "4" in the arguments False >>> i.has(0) # there *is* a "0" in the arguments True
Instead, use
containsto determine whether a number is in the interval or not:>>> i.contains(4) True >>> i.contains(0) False
Note that
expr.has(*patterns)is exactly equivalent toany(expr.has(p) for p in patterns). In particular,Falseis returned when the list of patterns is empty.>>> x.has() False
- has_free(*patterns)¶
Return True if self has object(s)
xas a free expression else False.Examples
>>> from sympy import Integral, Function >>> from sympy.abc import x, y >>> f = Function('f') >>> g = Function('g') >>> expr = Integral(f(x), (f(x), 1, g(y))) >>> expr.free_symbols {y} >>> expr.has_free(g(y)) True >>> expr.has_free(*(x, f(x))) False
This works for subexpressions and types, too:
>>> expr.has_free(g) True >>> (x + y + 1).has_free(y + 1) True
- has_xfree(s: set[Basic])¶
Return True if self has any of the patterns in s as a free argument, else False. This is like Basic.has_free but this will only report exact argument matches.
Examples
>>> from sympy import Function >>> from sympy.abc import x, y >>> f = Function('f') >>> f(x).has_xfree({f}) False >>> f(x).has_xfree({f(x)}) True >>> f(x + 1).has_xfree({x}) True >>> f(x + 1).has_xfree({x + 1}) True >>> f(x + y + 1).has_xfree({x + 1}) False
- integrate(*args, **kwargs)¶
See the integrate function in sympy.integrals
- invert(g, *gens, **args)¶
Return the multiplicative inverse of
selfmodgwhereself(andg) may be symbolic expressions).See also
sympy.core.numbers.mod_inverse,sympy.polys.polytools.invert
- is_Add = False¶
- is_AlgebraicNumber = False¶
- is_Atom = True¶
- is_Boolean = False¶
- is_Derivative = False¶
- is_Dummy = False¶
- is_Equality = False¶
- is_Float = False¶
- is_Function = False¶
- is_Indexed = False¶
- is_Integer = False¶
- is_MatAdd = False¶
- is_MatMul = False¶
- is_Matrix = False¶
- is_Mul = False¶
- is_Not = False¶
- is_Number = False¶
- is_NumberSymbol = False¶
- is_Order = False¶
- is_Piecewise = False¶
- is_Point = False¶
- is_Poly = False¶
- is_Pow = False¶
- is_Rational = False¶
- is_Relational = False¶
- is_Symbol = True¶
- is_Vector = False¶
- is_Wild = False¶
- property is_algebraic¶
- is_algebraic_expr(*syms)¶
This tests whether a given expression is algebraic or not, in the given symbols, syms. When syms is not given, all free symbols will be used. The rational function does not have to be in expanded or in any kind of canonical form.
This function returns False for expressions that are “algebraic expressions” with symbolic exponents. This is a simple extension to the is_rational_function, including rational exponentiation.
See also
References
Examples
>>> from sympy import Symbol, sqrt >>> x = Symbol('x', real=True) >>> sqrt(1 + x).is_rational_function() False >>> sqrt(1 + x).is_algebraic_expr() True
This function does not attempt any nontrivial simplifications that may result in an expression that does not appear to be an algebraic expression to become one.
>>> from sympy import exp, factor >>> a = sqrt(exp(x)**2 + 2*exp(x) + 1)/(exp(x) + 1) >>> a.is_algebraic_expr(x) False >>> factor(a).is_algebraic_expr() True
- property is_antihermitian¶
- property is_commutative¶
- is_comparable = False¶
- property is_complex¶
- property is_composite¶
- is_constant(*wrt, **flags)¶
Return True if self is constant, False if not, or None if the constancy could not be determined conclusively.
Examples
>>> from sympy import cos, sin, Sum, S, pi >>> from sympy.abc import a, n, x, y >>> x.is_constant() False >>> S(2).is_constant() True >>> Sum(x, (x, 1, 10)).is_constant() True >>> Sum(x, (x, 1, n)).is_constant() False >>> Sum(x, (x, 1, n)).is_constant(y) True >>> Sum(x, (x, 1, n)).is_constant(n) False >>> Sum(x, (x, 1, n)).is_constant(x) True >>> eq = a*cos(x)**2 + a*sin(x)**2 - a >>> eq.is_constant() True >>> eq.subs({x: pi, a: 2}) == eq.subs({x: pi, a: 3}) == 0 True
>>> (0**x).is_constant() False >>> x.is_constant() False >>> (x**x).is_constant() False >>> one = cos(x)**2 + sin(x)**2 >>> one.is_constant() True >>> ((one - 1)**(x + 1)).is_constant() in (True, False) # could be 0 or 1 True
- property is_even¶
- property is_extended_negative¶
- property is_extended_nonnegative¶
- property is_extended_nonpositive¶
- property is_extended_nonzero¶
- property is_extended_positive¶
- property is_extended_real¶
- property is_finite¶
- property is_hermitian¶
- is_hypergeometric(k)¶
- property is_imaginary¶
- property is_infinite¶
- property is_integer¶
- property is_irrational¶
- is_meromorphic(x, a)¶
This tests whether an expression is meromorphic as a function of the given symbol
xat the pointa.This method is intended as a quick test that will return None if no decision can be made without simplification or more detailed analysis.
Examples
>>> from sympy import zoo, log, sin, sqrt >>> from sympy.abc import x
>>> f = 1/x**2 + 1 - 2*x**3 >>> f.is_meromorphic(x, 0) True >>> f.is_meromorphic(x, 1) True >>> f.is_meromorphic(x, zoo) True
>>> g = x**log(3) >>> g.is_meromorphic(x, 0) False >>> g.is_meromorphic(x, 1) True >>> g.is_meromorphic(x, zoo) False
>>> h = sin(1/x)*x**2 >>> h.is_meromorphic(x, 0) False >>> h.is_meromorphic(x, 1) True >>> h.is_meromorphic(x, zoo) True
Multivalued functions are considered meromorphic when their branches are meromorphic. Thus most functions are meromorphic everywhere except at essential singularities and branch points. In particular, they will be meromorphic also on branch cuts except at their endpoints.
>>> log(x).is_meromorphic(x, -1) True >>> log(x).is_meromorphic(x, 0) False >>> sqrt(x).is_meromorphic(x, -1) True >>> sqrt(x).is_meromorphic(x, 0) False
- property is_negative¶
- property is_noninteger¶
- property is_nonnegative¶
- property is_nonpositive¶
- property is_nonzero¶
- is_number = False¶
- property is_odd¶
- property is_polar¶
- is_polynomial(*syms)¶
Return True if self is a polynomial in syms and False otherwise.
This checks if self is an exact polynomial in syms. This function returns False for expressions that are “polynomials” with symbolic exponents. Thus, you should be able to apply polynomial algorithms to expressions for which this returns True, and Poly(expr, *syms) should work if and only if expr.is_polynomial(*syms) returns True. The polynomial does not have to be in expanded form. If no symbols are given, all free symbols in the expression will be used.
This is not part of the assumptions system. You cannot do Symbol(‘z’, polynomial=True).
Examples
>>> from sympy import Symbol, Function >>> x = Symbol('x') >>> ((x**2 + 1)**4).is_polynomial(x) True >>> ((x**2 + 1)**4).is_polynomial() True >>> (2**x + 1).is_polynomial(x) False >>> (2**x + 1).is_polynomial(2**x) True >>> f = Function('f') >>> (f(x) + 1).is_polynomial(x) False >>> (f(x) + 1).is_polynomial(f(x)) True >>> (1/f(x) + 1).is_polynomial(f(x)) False
>>> n = Symbol('n', nonnegative=True, integer=True) >>> (x**n + 1).is_polynomial(x) False
This function does not attempt any nontrivial simplifications that may result in an expression that does not appear to be a polynomial to become one.
>>> from sympy import sqrt, factor, cancel >>> y = Symbol('y', positive=True) >>> a = sqrt(y**2 + 2*y + 1) >>> a.is_polynomial(y) False >>> factor(a) y + 1 >>> factor(a).is_polynomial(y) True
>>> b = (y**2 + 2*y + 1)/(y + 1) >>> b.is_polynomial(y) False >>> cancel(b) y + 1 >>> cancel(b).is_polynomial(y) True
See also .is_rational_function()
- property is_positive¶
- property is_prime¶
- property is_rational¶
- is_rational_function(*syms)¶
Test whether function is a ratio of two polynomials in the given symbols, syms. When syms is not given, all free symbols will be used. The rational function does not have to be in expanded or in any kind of canonical form.
This function returns False for expressions that are “rational functions” with symbolic exponents. Thus, you should be able to call .as_numer_denom() and apply polynomial algorithms to the result for expressions for which this returns True.
This is not part of the assumptions system. You cannot do Symbol(‘z’, rational_function=True).
Examples
>>> from sympy import Symbol, sin >>> from sympy.abc import x, y
>>> (x/y).is_rational_function() True
>>> (x**2).is_rational_function() True
>>> (x/sin(y)).is_rational_function(y) False
>>> n = Symbol('n', integer=True) >>> (x**n + 1).is_rational_function(x) False
This function does not attempt any nontrivial simplifications that may result in an expression that does not appear to be a rational function to become one.
>>> from sympy import sqrt, factor >>> y = Symbol('y', positive=True) >>> a = sqrt(y**2 + 2*y + 1)/y >>> a.is_rational_function(y) False >>> factor(a) (y + 1)/y >>> factor(a).is_rational_function(y) True
See also is_algebraic_expr().
- property is_real¶
- is_scalar = True¶
- is_symbol = True¶
- property is_transcendental¶
- property is_zero¶
- property kind¶
Default kind for all SymPy object. If the kind is not defined for the object, or if the object cannot infer the kind from its arguments, this will be returned.
Examples
>>> from sympy import Expr >>> Expr().kind UndefinedKind
- leadterm(x, logx=None, cdir=0)¶
Returns the leading term a*x**b as a tuple (a, b).
Examples
>>> from sympy.abc import x >>> (1+x+x**2).leadterm(x) (1, 0) >>> (1/x**2+x+x**2).leadterm(x) (1, -2)
- limit(x, xlim, dir='+')¶
Compute limit x->xlim.
- lseries(x=None, x0=0, dir='+', logx=None, cdir=0)¶
Wrapper for series yielding an iterator of the terms of the series.
Note: an infinite series will yield an infinite iterator. The following, for exaxmple, will never terminate. It will just keep printing terms of the sin(x) series:
for term in sin(x).lseries(x): print term
The advantage of lseries() over nseries() is that many times you are just interested in the next term in the series (i.e. the first term for example), but you do not know how many you should ask for in nseries() using the “n” parameter.
See also nseries().
- match(pattern, old=False)¶
Pattern matching.
Wild symbols match all.
Return
Nonewhen expression (self) does not match with pattern. Otherwise return a dictionary such that:pattern.xreplace(self.match(pattern)) == self
Examples
>>> from sympy import Wild, Sum >>> from sympy.abc import x, y >>> p = Wild("p") >>> q = Wild("q") >>> r = Wild("r") >>> e = (x+y)**(x+y) >>> e.match(p**p) {p_: x + y} >>> e.match(p**q) {p_: x + y, q_: x + y} >>> e = (2*x)**2 >>> e.match(p*q**r) {p_: 4, q_: x, r_: 2} >>> (p*q**r).xreplace(e.match(p*q**r)) 4*x**2
Structurally bound symbols are ignored during matching:
>>> Sum(x, (x, 1, 2)).match(Sum(y, (y, 1, p))) {p_: 2}
But they can be identified if desired:
>>> Sum(x, (x, 1, 2)).match(Sum(q, (q, 1, p))) {p_: 2, q_: x}
The
oldflag will give the old-style pattern matching where expressions and patterns are essentially solved to give the match. Both of the following give None unlessold=True:>>> (x - 2).match(p - x, old=True) {p_: 2*x - 2} >>> (2/x).match(p*x, old=True) {p_: 2/x**2}
- matches(expr, repl_dict=None, old=False)¶
Helper method for match() that looks for a match between Wild symbols in self and expressions in expr.
Examples
>>> from sympy import symbols, Wild, Basic >>> a, b, c = symbols('a b c') >>> x = Wild('x') >>> Basic(a + x, x).matches(Basic(a + b, c)) is None True >>> Basic(a + x, x).matches(Basic(a + b + c, b + c)) {x_: b + c}
- n(n=15, subs=None, maxn=100, chop=False, strict=False, quad=None, verbose=False)¶
Evaluate the given formula to an accuracy of n digits.
- Parameters:
- subsdict, optional
Substitute numerical values for symbols, e.g.
subs={x:3, y:1+pi}. The substitutions must be given as a dictionary.- maxnint, optional
Allow a maximum temporary working precision of maxn digits.
- chopbool or number, optional
Specifies how to replace tiny real or imaginary parts in subresults by exact zeros.
When
Truethe chop value defaults to standard precision.Otherwise the chop value is used to determine the magnitude of “small” for purposes of chopping.
>>> from sympy import N >>> x = 1e-4 >>> N(x, chop=True) 0.000100000000000000 >>> N(x, chop=1e-5) 0.000100000000000000 >>> N(x, chop=1e-4) 0
- strictbool, optional
Raise
PrecisionExhaustedif any subresult fails to evaluate to full accuracy, given the available maxprec.- quadstr, optional
Choose algorithm for numerical quadrature. By default, tanh-sinh quadrature is used. For oscillatory integrals on an infinite interval, try
quad='osc'.- verbosebool, optional
Print debug information.
Notes
When Floats are naively substituted into an expression, precision errors may adversely affect the result. For example, adding 1e16 (a Float) to 1 will truncate to 1e16; if 1e16 is then subtracted, the result will be 0. That is exactly what happens in the following:
>>> from sympy.abc import x, y, z >>> values = {x: 1e16, y: 1, z: 1e16} >>> (x + y - z).subs(values) 0
Using the subs argument for evalf is the accurate way to evaluate such an expression:
>>> (x + y - z).evalf(subs=values) 1.00000000000000
- name: str¶
- normal()¶
Return the expression as a fraction.
expression -> a/b
See also
as_numer_denomreturn
(a, b)instead ofa/b
- nseries(x=None, x0=0, n=6, dir='+', logx=None, cdir=0)¶
Wrapper to _eval_nseries if assumptions allow, else to series.
If x is given, x0 is 0, dir=’+’, and self has x, then _eval_nseries is called. This calculates “n” terms in the innermost expressions and then builds up the final series just by “cross-multiplying” everything out.
The optional
logxparameter can be used to replace any log(x) in the returned series with a symbolic value to avoid evaluating log(x) at 0. A symbol to use in place of log(x) should be provided.Advantage – it’s fast, because we do not have to determine how many terms we need to calculate in advance.
Disadvantage – you may end up with less terms than you may have expected, but the O(x**n) term appended will always be correct and so the result, though perhaps shorter, will also be correct.
If any of those assumptions is not met, this is treated like a wrapper to series which will try harder to return the correct number of terms.
See also lseries().
Examples
>>> from sympy import sin, log, Symbol >>> from sympy.abc import x, y >>> sin(x).nseries(x, 0, 6) x - x**3/6 + x**5/120 + O(x**6) >>> log(x+1).nseries(x, 0, 5) x - x**2/2 + x**3/3 - x**4/4 + O(x**5)
Handling of the
logxparameter — in the following example the expansion fails sincesindoes not have an asymptotic expansion at -oo (the limit of log(x) as x approaches 0):>>> e = sin(log(x)) >>> e.nseries(x, 0, 6) Traceback (most recent call last): ... PoleError: ... ... >>> logx = Symbol('logx') >>> e.nseries(x, 0, 6, logx=logx) sin(logx)
In the following example, the expansion works but only returns self unless the
logxparameter is used:>>> e = x**y >>> e.nseries(x, 0, 2) x**y >>> e.nseries(x, 0, 2, logx=logx) exp(logx*y)
- nsimplify(constants=(), tolerance=None, full=False)¶
See the nsimplify function in sympy.simplify
- powsimp(*args, **kwargs)¶
See the powsimp function in sympy.simplify
- primitive()¶
Return the positive Rational that can be extracted non-recursively from every term of self (i.e., self is treated like an Add). This is like the as_coeff_Mul() method but primitive always extracts a positive Rational (never a negative or a Float).
Examples
>>> from sympy.abc import x >>> (3*(x + 1)**2).primitive() (3, (x + 1)**2) >>> a = (6*x + 2); a.primitive() (2, 3*x + 1) >>> b = (x/2 + 3); b.primitive() (1/2, x + 6) >>> (a*b).primitive() == (1, a*b) True
- radsimp(**kwargs)¶
See the radsimp function in sympy.simplify
- ratsimp()¶
See the ratsimp function in sympy.simplify
- rcall(*args)¶
Apply on the argument recursively through the expression tree.
This method is used to simulate a common abuse of notation for operators. For instance, in SymPy the following will not work:
(x+Lambda(y, 2*y))(z) == x+2*z,however, you can use:
>>> from sympy import Lambda >>> from sympy.abc import x, y, z >>> (x + Lambda(y, 2*y)).rcall(z) x + 2*z
- refine(assumption=True)¶
See the refine function in sympy.assumptions
- removeO()¶
Removes the additive O(..) symbol if there is one
- replace(query, value, map=False, simultaneous=True, exact=None)¶
Replace matching subexpressions of
selfwithvalue.If
map = Truethen also return the mapping {old: new} whereoldwas a sub-expression found with query andnewis the replacement value for it. If the expression itself does not match the query, then the returned value will beself.xreplace(map)otherwise it should beself.subs(ordered(map.items())).Traverses an expression tree and performs replacement of matching subexpressions from the bottom to the top of the tree. The default approach is to do the replacement in a simultaneous fashion so changes made are targeted only once. If this is not desired or causes problems,
simultaneouscan be set to False.In addition, if an expression containing more than one Wild symbol is being used to match subexpressions and the
exactflag is None it will be set to True so the match will only succeed if all non-zero values are received for each Wild that appears in the match pattern. Setting this to False accepts a match of 0; while setting it True accepts all matches that have a 0 in them. See example below for cautions.The list of possible combinations of queries and replacement values is listed below:
See also
Examples
Initial setup
>>> from sympy import log, sin, cos, tan, Wild, Mul, Add >>> from sympy.abc import x, y >>> f = log(sin(x)) + tan(sin(x**2))
- 1.1. type -> type
obj.replace(type, newtype)
When object of type
typeis found, replace it with the result of passing its argument(s) tonewtype.>>> f.replace(sin, cos) log(cos(x)) + tan(cos(x**2)) >>> sin(x).replace(sin, cos, map=True) (cos(x), {sin(x): cos(x)}) >>> (x*y).replace(Mul, Add) x + y
- 1.2. type -> func
obj.replace(type, func)
When object of type
typeis found, applyfuncto its argument(s).funcmust be written to handle the number of arguments oftype.>>> f.replace(sin, lambda arg: sin(2*arg)) log(sin(2*x)) + tan(sin(2*x**2)) >>> (x*y).replace(Mul, lambda *args: sin(2*Mul(*args))) sin(2*x*y)
- 2.1. pattern -> expr
obj.replace(pattern(wild), expr(wild))
Replace subexpressions matching
patternwith the expression written in terms of the Wild symbols inpattern.>>> a, b = map(Wild, 'ab') >>> f.replace(sin(a), tan(a)) log(tan(x)) + tan(tan(x**2)) >>> f.replace(sin(a), tan(a/2)) log(tan(x/2)) + tan(tan(x**2/2)) >>> f.replace(sin(a), a) log(x) + tan(x**2) >>> (x*y).replace(a*x, a) y
Matching is exact by default when more than one Wild symbol is used: matching fails unless the match gives non-zero values for all Wild symbols:
>>> (2*x + y).replace(a*x + b, b - a) y - 2 >>> (2*x).replace(a*x + b, b - a) 2*x
When set to False, the results may be non-intuitive:
>>> (2*x).replace(a*x + b, b - a, exact=False) 2/x
- 2.2. pattern -> func
obj.replace(pattern(wild), lambda wild: expr(wild))
All behavior is the same as in 2.1 but now a function in terms of pattern variables is used rather than an expression:
>>> f.replace(sin(a), lambda a: sin(2*a)) log(sin(2*x)) + tan(sin(2*x**2))
- 3.1. func -> func
obj.replace(filter, func)
Replace subexpression
ewithfunc(e)iffilter(e)is True.>>> g = 2*sin(x**3) >>> g.replace(lambda expr: expr.is_Number, lambda expr: expr**2) 4*sin(x**9)
The expression itself is also targeted by the query but is done in such a fashion that changes are not made twice.
>>> e = x*(x*y + 1) >>> e.replace(lambda x: x.is_Mul, lambda x: 2*x) 2*x*(2*x*y + 1)
When matching a single symbol, exact will default to True, but this may or may not be the behavior that is desired:
Here, we want exact=False:
>>> from sympy import Function >>> f = Function('f') >>> e = f(1) + f(0) >>> q = f(a), lambda a: f(a + 1) >>> e.replace(*q, exact=False) f(1) + f(2) >>> e.replace(*q, exact=True) f(0) + f(2)
But here, the nature of matching makes selecting the right setting tricky:
>>> e = x**(1 + y) >>> (x**(1 + y)).replace(x**(1 + a), lambda a: x**-a, exact=False) x >>> (x**(1 + y)).replace(x**(1 + a), lambda a: x**-a, exact=True) x**(-x - y + 1) >>> (x**y).replace(x**(1 + a), lambda a: x**-a, exact=False) x >>> (x**y).replace(x**(1 + a), lambda a: x**-a, exact=True) x**(1 - y)
It is probably better to use a different form of the query that describes the target expression more precisely:
>>> (1 + x**(1 + y)).replace( ... lambda x: x.is_Pow and x.exp.is_Add and x.exp.args[0] == 1, ... lambda x: x.base**(1 - (x.exp - 1))) ... x**(1 - y) + 1
- rewrite(*args, deep=True, **hints)¶
Rewrite self using a defined rule.
Rewriting transforms an expression to another, which is mathematically equivalent but structurally different. For example you can rewrite trigonometric functions as complex exponentials or combinatorial functions as gamma function.
This method takes a pattern and a rule as positional arguments. pattern is optional parameter which defines the types of expressions that will be transformed. If it is not passed, all possible expressions will be rewritten. rule defines how the expression will be rewritten.
- Parameters:
- argsExpr
A rule, or pattern and rule. - pattern is a type or an iterable of types. - rule can be any object.
- deepbool, optional
If
True, subexpressions are recursively transformed. Default isTrue.
Examples
If pattern is unspecified, all possible expressions are transformed.
>>> from sympy import cos, sin, exp, I >>> from sympy.abc import x >>> expr = cos(x) + I*sin(x) >>> expr.rewrite(exp) exp(I*x)
Pattern can be a type or an iterable of types.
>>> expr.rewrite(sin, exp) exp(I*x)/2 + cos(x) - exp(-I*x)/2 >>> expr.rewrite([cos,], exp) exp(I*x)/2 + I*sin(x) + exp(-I*x)/2 >>> expr.rewrite([cos, sin], exp) exp(I*x)
Rewriting behavior can be implemented by defining
_eval_rewrite()method.>>> from sympy import Expr, sqrt, pi >>> class MySin(Expr): ... def _eval_rewrite(self, rule, args, **hints): ... x, = args ... if rule == cos: ... return cos(pi/2 - x, evaluate=False) ... if rule == sqrt: ... return sqrt(1 - cos(x)**2) >>> MySin(MySin(x)).rewrite(cos) cos(-cos(-x + pi/2) + pi/2) >>> MySin(x).rewrite(sqrt) sqrt(1 - cos(x)**2)
Defining
_eval_rewrite_as_[...]()method is supported for backwards compatibility reason. This may be removed in the future and using it is discouraged.>>> class MySin(Expr): ... def _eval_rewrite_as_cos(self, *args, **hints): ... x, = args ... return cos(pi/2 - x, evaluate=False) >>> MySin(x).rewrite(cos) cos(-x + pi/2)
- round(n=None)¶
Return x rounded to the given decimal place.
If a complex number would results, apply round to the real and imaginary components of the number.
Notes
The Python
roundfunction uses the SymPyroundmethod so it will always return a SymPy number (not a Python float or int):>>> isinstance(round(S(123), -2), Number) True
Examples
>>> from sympy import pi, E, I, S, Number >>> pi.round() 3 >>> pi.round(2) 3.14 >>> (2*pi + E*I).round() 6 + 3*I
The round method has a chopping effect:
>>> (2*pi + I/10).round() 6 >>> (pi/10 + 2*I).round() 2*I >>> (pi/10 + E*I).round(2) 0.31 + 2.72*I
- separate(deep=False, force=False)¶
See the separate function in sympy.simplify
- series(x=None, x0=0, n=6, dir='+', logx=None, cdir=0)¶
Series expansion of “self” around
x = x0yielding either terms of the series one by one (the lazy series given when n=None), else all the terms at once when n != None.Returns the series expansion of “self” around the point
x = x0with respect toxup toO((x - x0)**n, x, x0)(default n is 6).If
x=Noneandselfis univariate, the univariate symbol will be supplied, otherwise an error will be raised.- Parameters:
- exprExpression
The expression whose series is to be expanded.
- xSymbol
It is the variable of the expression to be calculated.
- x0Value
The value around which
xis calculated. Can be any value from-ootooo.- nValue
The value used to represent the order in terms of
x**n, up to which the series is to be expanded.- dirString, optional
The series-expansion can be bi-directional. If
dir="+", then (x->x0+). Ifdir="-", then (x->x0-). For infinite ``x0(ooor-oo), thedirargument is determined from the direction of the infinity (i.e.,dir="-"foroo).- logxoptional
It is used to replace any log(x) in the returned series with a symbolic value rather than evaluating the actual value.
- cdiroptional
It stands for complex direction, and indicates the direction from which the expansion needs to be evaluated.
- Returns:
- ExprExpression
Series expansion of the expression about x0
- Raises:
- TypeError
If “n” and “x0” are infinity objects
- PoleError
If “x0” is an infinity object
Examples
>>> from sympy import cos, exp, tan >>> from sympy.abc import x, y >>> cos(x).series() 1 - x**2/2 + x**4/24 + O(x**6) >>> cos(x).series(n=4) 1 - x**2/2 + O(x**4) >>> cos(x).series(x, x0=1, n=2) cos(1) - (x - 1)*sin(1) + O((x - 1)**2, (x, 1)) >>> e = cos(x + exp(y)) >>> e.series(y, n=2) cos(x + 1) - y*sin(x + 1) + O(y**2) >>> e.series(x, n=2) cos(exp(y)) - x*sin(exp(y)) + O(x**2)
If
n=Nonethen a generator of the series terms will be returned.>>> term=cos(x).series(n=None) >>> [next(term) for i in range(2)] [1, -x**2/2]
For
dir=+(default) the series is calculated from the right and fordir=-the series from the left. For smooth functions this flag will not alter the results.>>> abs(x).series(dir="+") x >>> abs(x).series(dir="-") -x >>> f = tan(x) >>> f.series(x, 2, 6, "+") tan(2) + (1 + tan(2)**2)*(x - 2) + (x - 2)**2*(tan(2)**3 + tan(2)) + (x - 2)**3*(1/3 + 4*tan(2)**2/3 + tan(2)**4) + (x - 2)**4*(tan(2)**5 + 5*tan(2)**3/3 + 2*tan(2)/3) + (x - 2)**5*(2/15 + 17*tan(2)**2/15 + 2*tan(2)**4 + tan(2)**6) + O((x - 2)**6, (x, 2))
>>> f.series(x, 2, 3, "-") tan(2) + (2 - x)*(-tan(2)**2 - 1) + (2 - x)**2*(tan(2)**3 + tan(2)) + O((x - 2)**3, (x, 2))
For rational expressions this method may return original expression without the Order term. >>> (1/x).series(x, n=8) 1/x
- simplify(**kwargs)¶
See the simplify function in sympy.simplify
- sort_key(order=None)¶
Return a sort key.
Examples
>>> from sympy import S, I
>>> sorted([S(1)/2, I, -I], key=lambda x: x.sort_key()) [1/2, -I, I]
>>> S("[x, 1/x, 1/x**2, x**2, x**(1/2), x**(1/4), x**(3/2)]") [x, 1/x, x**(-2), x**2, sqrt(x), x**(1/4), x**(3/2)] >>> sorted(_, key=lambda x: x.sort_key()) [x**(-2), 1/x, x**(1/4), sqrt(x), x, x**(3/2), x**2]
- subs(*args, **kwargs)¶
Substitutes old for new in an expression after sympifying args.
- args is either:
two arguments, e.g. foo.subs(old, new)
- one iterable argument, e.g. foo.subs(iterable). The iterable may be
- o an iterable container with (old, new) pairs. In this case the
replacements are processed in the order given with successive patterns possibly affecting replacements already made.
- o a dict or set whose key/value items correspond to old/new pairs.
In this case the old/new pairs will be sorted by op count and in case of a tie, by number of args and the default_sort_key. The resulting sorted list is then processed as an iterable container (see previous).
If the keyword
simultaneousis True, the subexpressions will not be evaluated until all the substitutions have been made.See also
Examples
>>> from sympy import pi, exp, limit, oo >>> from sympy.abc import x, y >>> (1 + x*y).subs(x, pi) pi*y + 1 >>> (1 + x*y).subs({x:pi, y:2}) 1 + 2*pi >>> (1 + x*y).subs([(x, pi), (y, 2)]) 1 + 2*pi >>> reps = [(y, x**2), (x, 2)] >>> (x + y).subs(reps) 6 >>> (x + y).subs(reversed(reps)) x**2 + 2
>>> (x**2 + x**4).subs(x**2, y) y**2 + y
To replace only the x**2 but not the x**4, use xreplace:
>>> (x**2 + x**4).xreplace({x**2: y}) x**4 + y
To delay evaluation until all substitutions have been made, set the keyword
simultaneousto True:>>> (x/y).subs([(x, 0), (y, 0)]) 0 >>> (x/y).subs([(x, 0), (y, 0)], simultaneous=True) nan
This has the added feature of not allowing subsequent substitutions to affect those already made:
>>> ((x + y)/y).subs({x + y: y, y: x + y}) 1 >>> ((x + y)/y).subs({x + y: y, y: x + y}, simultaneous=True) y/(x + y)
In order to obtain a canonical result, unordered iterables are sorted by count_op length, number of arguments and by the default_sort_key to break any ties. All other iterables are left unsorted.
>>> from sympy import sqrt, sin, cos >>> from sympy.abc import a, b, c, d, e
>>> A = (sqrt(sin(2*x)), a) >>> B = (sin(2*x), b) >>> C = (cos(2*x), c) >>> D = (x, d) >>> E = (exp(x), e)
>>> expr = sqrt(sin(2*x))*sin(exp(x)*x)*cos(2*x) + sin(2*x)
>>> expr.subs(dict([A, B, C, D, E])) a*c*sin(d*e) + b
The resulting expression represents a literal replacement of the old arguments with the new arguments. This may not reflect the limiting behavior of the expression:
>>> (x**3 - 3*x).subs({x: oo}) nan
>>> limit(x**3 - 3*x, x, oo) oo
If the substitution will be followed by numerical evaluation, it is better to pass the substitution to evalf as
>>> (1/x).evalf(subs={x: 3.0}, n=21) 0.333333333333333333333
rather than
>>> (1/x).subs({x: 3.0}).evalf(21) 0.333333333333333314830
as the former will ensure that the desired level of precision is obtained.
- taylor_term(n, x, *previous_terms)¶
General method for the taylor term.
This method is slow, because it differentiates n-times. Subclasses can redefine it to make it faster by using the “previous_terms”.
- to_nnf(simplify=True)¶
- together(*args, **kwargs)¶
See the together function in sympy.polys
- transpose()¶
- trigsimp(**args)¶
See the trigsimp function in sympy.simplify
- xreplace(rule, hack2=False)¶
Replace occurrences of objects within the expression.
- Parameters:
- ruledict-like
Expresses a replacement rule
- Returns:
- xreplacethe result of the replacement
See also
Examples
>>> from sympy import symbols, pi, exp >>> x, y, z = symbols('x y z') >>> (1 + x*y).xreplace({x: pi}) pi*y + 1 >>> (1 + x*y).xreplace({x: pi, y: 2}) 1 + 2*pi
Replacements occur only if an entire node in the expression tree is matched:
>>> (x*y + z).xreplace({x*y: pi}) z + pi >>> (x*y*z).xreplace({x*y: pi}) x*y*z >>> (2*x).xreplace({2*x: y, x: z}) y >>> (2*2*x).xreplace({2*x: y, x: z}) 4*z >>> (x + y + 2).xreplace({x + y: 2}) x + y + 2 >>> (x + 2 + exp(x + 2)).xreplace({x + 2: y}) x + exp(y) + 2
xreplace does not differentiate between free and bound symbols. In the following, subs(x, y) would not change x since it is a bound symbol, but xreplace does:
>>> from sympy import Integral >>> Integral(x, (x, 1, 2*x)).xreplace({x: y}) Integral(y, (y, 1, 2*y))
Trying to replace x with an expression raises an error:
>>> Integral(x, (x, 1, 2*x)).xreplace({x: 2*y}) ValueError: Invalid limits given: ((2*y, 1, 4*y),)
Formula¶
- class nipy.algorithms.statistics.formula.formulae.Formula(seq, char='b')¶
Bases:
objectA Formula is a model for a mean in a regression model.
It is often given by a sequence of sympy expressions, with the mean model being the sum of each term multiplied by a linear regression coefficient.
The expressions may depend on additional Symbol instances, giving a non-linear regression model.
- __init__(seq, char='b')¶
- Parameters:
- seqsequence of
sympy.Basic - charstr, optional
character for regression coefficient
- seqsequence of
- property coefs¶
Coefficients in the linear regression formula.
- design(input, param=None, return_float=False, contrasts=None)¶
Construct the design matrix, and optional contrast matrices.
- Parameters:
- inputnp.recarray
Recarray including fields needed to compute the Terms in getparams(self.design_expr).
- paramNone or np.recarray
Recarray including fields that are not Terms in getparams(self.design_expr)
- return_floatbool, optional
If True, return a np.float64 array rather than a np.recarray
- contrastsNone or dict, optional
Contrasts. The items in this dictionary should be (str, Formula) pairs where a contrast matrix is constructed for each Formula by evaluating its design at the same parameters as self.design. If not None, then the return_float is set to True.
- Returns:
- des2D array
design matrix
- cmatricesdict, optional
Dictionary with keys from contrasts input, and contrast matrices corresponding to des design matrix. Returned only if contrasts input is not None
- property design_expr¶
- property dtype¶
The dtype of the design matrix of the Formula.
- static fromrec(rec, keep=[], drop=[])¶
Construct Formula from recarray
For fields with a string-dtype, it is assumed that these are qualtiatitve regressors, i.e. Factors.
- Parameters:
- rec: recarray
Recarray whose field names will be used to create a formula.
- keep: []
Field names to explicitly keep, dropping all others.
- drop: []
Field names to drop.
- property mean¶
Expression for the mean, expressed as a linear combination of terms, each with dummy variables in front.
- property params¶
The parameters in the Formula.
- subs(old, new)¶
Perform a sympy substitution on all terms in the Formula
Returns a new instance of the same class
- Parameters:
- oldsympy.Basic
The expression to be changed
- newsympy.Basic
The value to change it to.
- Returns:
- newfFormula
Examples
>>> s, t = [Term(l) for l in 'st'] >>> f, g = [sympy.Function(l) for l in 'fg'] >>> form = Formula([f(t),g(s)]) >>> newform = form.subs(g, sympy.Function('h')) >>> newform.terms array([f(t), h(s)], dtype=object) >>> form.terms array([f(t), g(s)], dtype=object)
- property terms¶
Terms in the linear regression formula.
RandomEffects¶
- class nipy.algorithms.statistics.formula.formulae.RandomEffects(seq, sigma=None, char='e')¶
Bases:
FormulaCovariance matrices for common random effects analyses.
Examples
Two subjects (here named 2 and 3):
>>> subj = make_recarray([2,2,2,3,3], 's') >>> subj_factor = Factor('s', [2,3])
By default the covariance matrix is symbolic. The display differs a little between sympy versions (hence we don’t check it in the doctests):
>>> c = RandomEffects(subj_factor.terms) >>> c.cov(subj) array([[_s2_0, _s2_0, _s2_0, 0, 0], [_s2_0, _s2_0, _s2_0, 0, 0], [_s2_0, _s2_0, _s2_0, 0, 0], [0, 0, 0, _s2_1, _s2_1], [0, 0, 0, _s2_1, _s2_1]], dtype=object)
With a numeric sigma, you get a numeric array:
>>> c = RandomEffects(subj_factor.terms, sigma=np.array([[4,1],[1,6]])) >>> c.cov(subj) array([[ 4., 4., 4., 1., 1.], [ 4., 4., 4., 1., 1.], [ 4., 4., 4., 1., 1.], [ 1., 1., 1., 6., 6.], [ 1., 1., 1., 6., 6.]])
- __init__(seq, sigma=None, char='e')¶
Initialize random effects instance
- Parameters:
- seq[
sympy.Basic] - sigmandarray
Covariance of the random effects. Defaults to a diagonal with entries for each random effect.
- charcharacter for regression coefficient
- seq[
- property coefs¶
Coefficients in the linear regression formula.
- cov(term, param=None)¶
Compute the covariance matrix for some given data.
- Parameters:
- termnp.recarray
Recarray including fields corresponding to the Terms in getparams(self.design_expr).
- paramnp.recarray
Recarray including fields that are not Terms in getparams(self.design_expr)
- Returns:
- Cndarray
Covariance matrix implied by design and self.sigma.
- design(input, param=None, return_float=False, contrasts=None)¶
Construct the design matrix, and optional contrast matrices.
- Parameters:
- inputnp.recarray
Recarray including fields needed to compute the Terms in getparams(self.design_expr).
- paramNone or np.recarray
Recarray including fields that are not Terms in getparams(self.design_expr)
- return_floatbool, optional
If True, return a np.float64 array rather than a np.recarray
- contrastsNone or dict, optional
Contrasts. The items in this dictionary should be (str, Formula) pairs where a contrast matrix is constructed for each Formula by evaluating its design at the same parameters as self.design. If not None, then the return_float is set to True.
- Returns:
- des2D array
design matrix
- cmatricesdict, optional
Dictionary with keys from contrasts input, and contrast matrices corresponding to des design matrix. Returned only if contrasts input is not None
- property design_expr¶
- property dtype¶
The dtype of the design matrix of the Formula.
- static fromrec(rec, keep=[], drop=[])¶
Construct Formula from recarray
For fields with a string-dtype, it is assumed that these are qualtiatitve regressors, i.e. Factors.
- Parameters:
- rec: recarray
Recarray whose field names will be used to create a formula.
- keep: []
Field names to explicitly keep, dropping all others.
- drop: []
Field names to drop.
- property mean¶
Expression for the mean, expressed as a linear combination of terms, each with dummy variables in front.
- property params¶
The parameters in the Formula.
- subs(old, new)¶
Perform a sympy substitution on all terms in the Formula
Returns a new instance of the same class
- Parameters:
- oldsympy.Basic
The expression to be changed
- newsympy.Basic
The value to change it to.
- Returns:
- newfFormula
Examples
>>> s, t = [Term(l) for l in 'st'] >>> f, g = [sympy.Function(l) for l in 'fg'] >>> form = Formula([f(t),g(s)]) >>> newform = form.subs(g, sympy.Function('h')) >>> newform.terms array([f(t), h(s)], dtype=object) >>> form.terms array([f(t), g(s)], dtype=object)
- property terms¶
Terms in the linear regression formula.
Term¶
- class nipy.algorithms.statistics.formula.formulae.Term(name, **assumptions)¶
Bases:
SymbolA sympy.Symbol type to represent a term an a regression model
Terms can be added to other sympy expressions with the single convention that a term plus itself returns itself.
It is meant to emulate something on the right hand side of a formula in R. In particular, its name can be the name of a field in a recarray used to create a design matrix.
>>> t = Term('x') >>> xval = np.array([(3,),(4,),(5,)], np.dtype([('x', np.float64)])) >>> f = t.formula >>> d = f.design(xval) >>> print(d.dtype.descr) [('x', '<f8')] >>> f.design(xval, return_float=True) array([ 3., 4., 5.])
- __init__(*args, **kwargs)¶
- adjoint()¶
- apart(x=None, **args)¶
See the apart function in sympy.polys
- property args: tuple[Basic, ...]¶
Returns a tuple of arguments of ‘self’.
Notes
Never use self._args, always use self.args. Only use _args in __new__ when creating a new function. Do not override .args() from Basic (so that it is easy to change the interface in the future if needed).
Examples
>>> from sympy import cot >>> from sympy.abc import x, y
>>> cot(x).args (x,)
>>> cot(x).args[0] x
>>> (x*y).args (x, y)
>>> (x*y).args[1] y
- args_cnc(cset=False, warn=True, split_1=True)¶
Return [commutative factors, non-commutative factors] of self.
Examples
>>> from sympy import symbols, oo >>> A, B = symbols('A B', commutative=0) >>> x, y = symbols('x y') >>> (-2*x*y).args_cnc() [[-1, 2, x, y], []] >>> (-2.5*x).args_cnc() [[-1, 2.5, x], []] >>> (-2*x*A*B*y).args_cnc() [[-1, 2, x, y], [A, B]] >>> (-2*x*A*B*y).args_cnc(split_1=False) [[-2, x, y], [A, B]] >>> (-2*x*y).args_cnc(cset=True) [{-1, 2, x, y}, []]
The arg is always treated as a Mul:
>>> (-2 + x + A).args_cnc() [[], [x - 2 + A]] >>> (-oo).args_cnc() # -oo is a singleton [[-1, oo], []]
- as_base_exp() tuple[Expr, Expr]¶
- as_coeff_Add(rational=False) tuple[Number, Expr]¶
Efficiently extract the coefficient of a summation.
- as_coeff_Mul(rational: bool = False) tuple[Number, Expr]¶
Efficiently extract the coefficient of a product.
- as_coeff_add(*deps) tuple[Expr, tuple[Expr, ...]]¶
Return the tuple (c, args) where self is written as an Add,
a.c should be a Rational added to any terms of the Add that are independent of deps.
args should be a tuple of all other terms of
a; args is empty if self is a Number or if self is independent of deps (when given).This should be used when you do not know if self is an Add or not but you want to treat self as an Add or if you want to process the individual arguments of the tail of self as an Add.
if you know self is an Add and want only the head, use self.args[0];
if you do not want to process the arguments of the tail but need the tail then use self.as_two_terms() which gives the head and tail.
if you want to split self into an independent and dependent parts use
self.as_independent(*deps)
>>> from sympy import S >>> from sympy.abc import x, y >>> (S(3)).as_coeff_add() (3, ()) >>> (3 + x).as_coeff_add() (3, (x,)) >>> (3 + x + y).as_coeff_add(x) (y + 3, (x,)) >>> (3 + y).as_coeff_add(x) (y + 3, ())
- as_coeff_exponent(x) tuple[Expr, Expr]¶
c*x**e -> c,ewhere x can be any symbolic expression.
- as_coeff_mul(*deps, **kwargs) tuple[Expr, tuple[Expr, ...]]¶
Return the tuple (c, args) where self is written as a Mul,
m.c should be a Rational multiplied by any factors of the Mul that are independent of deps.
args should be a tuple of all other factors of m; args is empty if self is a Number or if self is independent of deps (when given).
This should be used when you do not know if self is a Mul or not but you want to treat self as a Mul or if you want to process the individual arguments of the tail of self as a Mul.
if you know self is a Mul and want only the head, use self.args[0];
if you do not want to process the arguments of the tail but need the tail then use self.as_two_terms() which gives the head and tail;
if you want to split self into an independent and dependent parts use
self.as_independent(*deps)
>>> from sympy import S >>> from sympy.abc import x, y >>> (S(3)).as_coeff_mul() (3, ()) >>> (3*x*y).as_coeff_mul() (3, (x, y)) >>> (3*x*y).as_coeff_mul(x) (3*y, (x,)) >>> (3*y).as_coeff_mul(x) (3*y, ())
- as_coefficient(expr)¶
Extracts symbolic coefficient at the given expression. In other words, this functions separates ‘self’ into the product of ‘expr’ and ‘expr’-free coefficient. If such separation is not possible it will return None.
See also
coeffreturn sum of terms have a given factor
as_coeff_Addseparate the additive constant from an expression
as_coeff_Mulseparate the multiplicative constant from an expression
as_independentseparate x-dependent terms/factors from others
sympy.polys.polytools.Poly.coeff_monomialefficiently find the single coefficient of a monomial in Poly
sympy.polys.polytools.Poly.nthlike coeff_monomial but powers of monomial terms are used
Examples
>>> from sympy import E, pi, sin, I, Poly >>> from sympy.abc import x
>>> E.as_coefficient(E) 1 >>> (2*E).as_coefficient(E) 2 >>> (2*sin(E)*E).as_coefficient(E)
Two terms have E in them so a sum is returned. (If one were desiring the coefficient of the term exactly matching E then the constant from the returned expression could be selected. Or, for greater precision, a method of Poly can be used to indicate the desired term from which the coefficient is desired.)
>>> (2*E + x*E).as_coefficient(E) x + 2 >>> _.args[0] # just want the exact match 2 >>> p = Poly(2*E + x*E); p Poly(x*E + 2*E, x, E, domain='ZZ') >>> p.coeff_monomial(E) 2 >>> p.nth(0, 1) 2
Since the following cannot be written as a product containing E as a factor, None is returned. (If the coefficient
2*xis desired then thecoeffmethod should be used.)>>> (2*E*x + x).as_coefficient(E) >>> (2*E*x + x).coeff(E) 2*x
>>> (E*(x + 1) + x).as_coefficient(E)
>>> (2*pi*I).as_coefficient(pi*I) 2 >>> (2*I).as_coefficient(pi*I)
- as_coefficients_dict(*syms)¶
Return a dictionary mapping terms to their Rational coefficient. Since the dictionary is a defaultdict, inquiries about terms which were not present will return a coefficient of 0.
If symbols
symsare provided, any multiplicative terms independent of them will be considered a coefficient and a regular dictionary of syms-dependent generators as keys and their corresponding coefficients as values will be returned.Examples
>>> from sympy.abc import a, x, y >>> (3*x + a*x + 4).as_coefficients_dict() {1: 4, x: 3, a*x: 1} >>> _[a] 0 >>> (3*a*x).as_coefficients_dict() {a*x: 3} >>> (3*a*x).as_coefficients_dict(x) {x: 3*a} >>> (3*a*x).as_coefficients_dict(y) {1: 3*a*x}
- as_content_primitive(radical=False, clear=True)¶
This method should recursively remove a Rational from all arguments and return that (content) and the new self (primitive). The content should always be positive and
Mul(*foo.as_content_primitive()) == foo. The primitive need not be in canonical form and should try to preserve the underlying structure if possible (i.e. expand_mul should not be applied to self).Examples
>>> from sympy import sqrt >>> from sympy.abc import x, y, z
>>> eq = 2 + 2*x + 2*y*(3 + 3*y)
The as_content_primitive function is recursive and retains structure:
>>> eq.as_content_primitive() (2, x + 3*y*(y + 1) + 1)
Integer powers will have Rationals extracted from the base:
>>> ((2 + 6*x)**2).as_content_primitive() (4, (3*x + 1)**2) >>> ((2 + 6*x)**(2*y)).as_content_primitive() (1, (2*(3*x + 1))**(2*y))
Terms may end up joining once their as_content_primitives are added:
>>> ((5*(x*(1 + y)) + 2*x*(3 + 3*y))).as_content_primitive() (11, x*(y + 1)) >>> ((3*(x*(1 + y)) + 2*x*(3 + 3*y))).as_content_primitive() (9, x*(y + 1)) >>> ((3*(z*(1 + y)) + 2.0*x*(3 + 3*y))).as_content_primitive() (1, 6.0*x*(y + 1) + 3*z*(y + 1)) >>> ((5*(x*(1 + y)) + 2*x*(3 + 3*y))**2).as_content_primitive() (121, x**2*(y + 1)**2) >>> ((x*(1 + y) + 0.4*x*(3 + 3*y))**2).as_content_primitive() (1, 4.84*x**2*(y + 1)**2)
Radical content can also be factored out of the primitive:
>>> (2*sqrt(2) + 4*sqrt(10)).as_content_primitive(radical=True) (2, sqrt(2)*(1 + 2*sqrt(5)))
If clear=False (default is True) then content will not be removed from an Add if it can be distributed to leave one or more terms with integer coefficients.
>>> (x/2 + y).as_content_primitive() (1/2, x + 2*y) >>> (x/2 + y).as_content_primitive(clear=False) (1, x/2 + y)
- as_dummy()¶
Return the expression with any objects having structurally bound symbols replaced with unique, canonical symbols within the object in which they appear and having only the default assumption for commutativity being True. When applied to a symbol a new symbol having only the same commutativity will be returned.
Notes
Any object that has structurally bound variables should have a property, bound_symbols that returns those symbols appearing in the object.
Examples
>>> from sympy import Integral, Symbol >>> from sympy.abc import x >>> r = Symbol('r', real=True) >>> Integral(r, (r, x)).as_dummy() Integral(_0, (_0, x)) >>> _.variables[0].is_real is None True >>> r.as_dummy() _r
- as_expr(*gens)¶
Convert a polynomial to a SymPy expression.
Examples
>>> from sympy import sin >>> from sympy.abc import x, y
>>> f = (x**2 + x*y).as_poly(x, y) >>> f.as_expr() x**2 + x*y
>>> sin(x).as_expr() sin(x)
- as_independent(*deps, **hint) tuple[Expr, Expr]¶
A mostly naive separation of a Mul or Add into arguments that are not are dependent on deps. To obtain as complete a separation of variables as possible, use a separation method first, e.g.:
separatevars() to change Mul, Add and Pow (including exp) into Mul
.expand(mul=True) to change Add or Mul into Add
.expand(log=True) to change log expr into an Add
The only non-naive thing that is done here is to respect noncommutative ordering of variables and to always return (0, 0) for self of zero regardless of hints.
For nonzero self, the returned tuple (i, d) has the following interpretation:
i will has no variable that appears in deps
d will either have terms that contain variables that are in deps, or be equal to 0 (when self is an Add) or 1 (when self is a Mul)
if self is an Add then self = i + d
if self is a Mul then self = i*d
otherwise (self, S.One) or (S.One, self) is returned.
To force the expression to be treated as an Add, use the hint as_Add=True
See also
separatevarsexpand_logsympy.core.add.Add.as_two_termssympy.core.mul.Mul.as_two_termsas_coeff_mul
Examples
– self is an Add
>>> from sympy import sin, cos, exp >>> from sympy.abc import x, y, z
>>> (x + x*y).as_independent(x) (0, x*y + x) >>> (x + x*y).as_independent(y) (x, x*y) >>> (2*x*sin(x) + y + x + z).as_independent(x) (y + z, 2*x*sin(x) + x) >>> (2*x*sin(x) + y + x + z).as_independent(x, y) (z, 2*x*sin(x) + x + y)
– self is a Mul
>>> (x*sin(x)*cos(y)).as_independent(x) (cos(y), x*sin(x))
non-commutative terms cannot always be separated out when self is a Mul
>>> from sympy import symbols >>> n1, n2, n3 = symbols('n1 n2 n3', commutative=False) >>> (n1 + n1*n2).as_independent(n2) (n1, n1*n2) >>> (n2*n1 + n1*n2).as_independent(n2) (0, n1*n2 + n2*n1) >>> (n1*n2*n3).as_independent(n1) (1, n1*n2*n3) >>> (n1*n2*n3).as_independent(n2) (n1, n2*n3) >>> ((x-n1)*(x-y)).as_independent(x) (1, (x - y)*(x - n1))
– self is anything else:
>>> (sin(x)).as_independent(x) (1, sin(x)) >>> (sin(x)).as_independent(y) (sin(x), 1) >>> exp(x+y).as_independent(x) (1, exp(x + y))
– force self to be treated as an Add:
>>> (3*x).as_independent(x, as_Add=True) (0, 3*x)
– force self to be treated as a Mul:
>>> (3+x).as_independent(x, as_Add=False) (1, x + 3) >>> (-3+x).as_independent(x, as_Add=False) (1, x - 3)
Note how the below differs from the above in making the constant on the dep term positive.
>>> (y*(-3+x)).as_independent(x) (y, x - 3)
- – use .as_independent() for true independence testing instead
of .has(). The former considers only symbols in the free symbols while the latter considers all symbols
>>> from sympy import Integral >>> I = Integral(x, (x, 1, 2)) >>> I.has(x) True >>> x in I.free_symbols False >>> I.as_independent(x) == (I, 1) True >>> (I + x).as_independent(x) == (I, x) True
Note: when trying to get independent terms, a separation method might need to be used first. In this case, it is important to keep track of what you send to this routine so you know how to interpret the returned values
>>> from sympy import separatevars, log >>> separatevars(exp(x+y)).as_independent(x) (exp(y), exp(x)) >>> (x + x*y).as_independent(y) (x, x*y) >>> separatevars(x + x*y).as_independent(y) (x, y + 1) >>> (x*(1 + y)).as_independent(y) (x, y + 1) >>> (x*(1 + y)).expand(mul=True).as_independent(y) (x, x*y) >>> a, b=symbols('a b', positive=True) >>> (log(a*b).expand(log=True)).as_independent(b) (log(a), log(b))
- as_leading_term(*symbols, logx=None, cdir=0)¶
Returns the leading (nonzero) term of the series expansion of self.
The _eval_as_leading_term routines are used to do this, and they must always return a non-zero value.
Examples
>>> from sympy.abc import x >>> (1 + x + x**2).as_leading_term(x) 1 >>> (1/x**2 + x + x**2).as_leading_term(x) x**(-2)
- as_numer_denom()¶
Return the numerator and the denominator of an expression.
expression -> a/b -> a, b
This is just a stub that should be defined by an object’s class methods to get anything else.
See also
normalreturn
a/binstead of(a, b)
- as_ordered_factors(order=None)¶
Return list of ordered factors (if Mul) else [self].
- as_ordered_terms(order=None, data=False)¶
Transform an expression to an ordered list of terms.
Examples
>>> from sympy import sin, cos >>> from sympy.abc import x
>>> (sin(x)**2*cos(x) + sin(x)**2 + 1).as_ordered_terms() [sin(x)**2*cos(x), sin(x)**2, 1]
- as_poly(*gens, **args)¶
Converts
selfto a polynomial or returnsNone.
- as_powers_dict()¶
Return self as a dictionary of factors with each factor being treated as a power. The keys are the bases of the factors and the values, the corresponding exponents. The resulting dictionary should be used with caution if the expression is a Mul and contains non- commutative factors since the order that they appeared will be lost in the dictionary.
See also
as_ordered_factorsAn alternative for noncommutative applications, returning an ordered list of factors.
args_cncSimilar to as_ordered_factors, but guarantees separation of commutative and noncommutative factors.
- as_real_imag(deep=True, **hints)¶
Performs complex expansion on ‘self’ and returns a tuple containing collected both real and imaginary parts. This method cannot be confused with re() and im() functions, which does not perform complex expansion at evaluation.
However it is possible to expand both re() and im() functions and get exactly the same results as with a single call to this function.
>>> from sympy import symbols, I
>>> x, y = symbols('x,y', real=True)
>>> (x + y*I).as_real_imag() (x, y)
>>> from sympy.abc import z, w
>>> (z + w*I).as_real_imag() (re(z) - im(w), re(w) + im(z))
- as_set()¶
Rewrites Boolean expression in terms of real sets.
Examples
>>> from sympy import Symbol, Eq, Or, And >>> x = Symbol('x', real=True) >>> Eq(x, 0).as_set() {0} >>> (x > 0).as_set() Interval.open(0, oo) >>> And(-2 < x, x < 2).as_set() Interval.open(-2, 2) >>> Or(x < -2, 2 < x).as_set() Union(Interval.open(-oo, -2), Interval.open(2, oo))
- as_terms()¶
Transform an expression to a list of terms.
- aseries(x=None, n=6, bound=0, hir=False)¶
Asymptotic Series expansion of self. This is equivalent to
self.series(x, oo, n).- Parameters:
- selfExpression
The expression whose series is to be expanded.
- xSymbol
It is the variable of the expression to be calculated.
- nValue
The value used to represent the order in terms of
x**n, up to which the series is to be expanded.- hirBoolean
Set this parameter to be True to produce hierarchical series. It stops the recursion at an early level and may provide nicer and more useful results.
- boundValue, Integer
Use the
boundparameter to give limit on rewriting coefficients in its normalised form.
- Returns:
- Expr
Asymptotic series expansion of the expression.
See also
Expr.aseriesSee the docstring of this function for complete details of this wrapper.
Notes
This algorithm is directly induced from the limit computational algorithm provided by Gruntz. It majorly uses the mrv and rewrite sub-routines. The overall idea of this algorithm is first to look for the most rapidly varying subexpression w of a given expression f and then expands f in a series in w. Then same thing is recursively done on the leading coefficient till we get constant coefficients.
If the most rapidly varying subexpression of a given expression f is f itself, the algorithm tries to find a normalised representation of the mrv set and rewrites f using this normalised representation.
If the expansion contains an order term, it will be either
O(x ** (-n))orO(w ** (-n))wherewbelongs to the most rapidly varying expression ofself.References
[1]Gruntz, Dominik. A new algorithm for computing asymptotic series. In: Proc. 1993 Int. Symp. Symbolic and Algebraic Computation. 1993. pp. 239-244.
[2]Gruntz thesis - p90
Examples
>>> from sympy import sin, exp >>> from sympy.abc import x
>>> e = sin(1/x + exp(-x)) - sin(1/x)
>>> e.aseries(x) (1/(24*x**4) - 1/(2*x**2) + 1 + O(x**(-6), (x, oo)))*exp(-x)
>>> e.aseries(x, n=3, hir=True) -exp(-2*x)*sin(1/x)/2 + exp(-x)*cos(1/x) + O(exp(-3*x), (x, oo))
>>> e = exp(exp(x)/(1 - 1/x))
>>> e.aseries(x) exp(exp(x)/(1 - 1/x))
>>> e.aseries(x, bound=3) exp(exp(x)/x**2)*exp(exp(x)/x)*exp(-exp(x) + exp(x)/(1 - 1/x) - exp(x)/x - exp(x)/x**2)*exp(exp(x))
For rational expressions this method may return original expression without the Order term. >>> (1/x).aseries(x, n=8) 1/x
- property assumptions0¶
Return object type assumptions.
For example:
Symbol(‘x’, real=True) Symbol(‘x’, integer=True)
are different objects. In other words, besides Python type (Symbol in this case), the initial assumptions are also forming their typeinfo.
Examples
>>> from sympy import Symbol >>> from sympy.abc import x >>> x.assumptions0 {'commutative': True} >>> x = Symbol("x", positive=True) >>> x.assumptions0 {'commutative': True, 'complex': True, 'extended_negative': False, 'extended_nonnegative': True, 'extended_nonpositive': False, 'extended_nonzero': True, 'extended_positive': True, 'extended_real': True, 'finite': True, 'hermitian': True, 'imaginary': False, 'infinite': False, 'negative': False, 'nonnegative': True, 'nonpositive': False, 'nonzero': True, 'positive': True, 'real': True, 'zero': False}
- atoms(*types)¶
Returns the atoms that form the current object.
By default, only objects that are truly atomic and cannot be divided into smaller pieces are returned: symbols, numbers, and number symbols like I and pi. It is possible to request atoms of any type, however, as demonstrated below.
Examples
>>> from sympy import I, pi, sin >>> from sympy.abc import x, y >>> (1 + x + 2*sin(y + I*pi)).atoms() {1, 2, I, pi, x, y}
If one or more types are given, the results will contain only those types of atoms.
>>> from sympy import Number, NumberSymbol, Symbol >>> (1 + x + 2*sin(y + I*pi)).atoms(Symbol) {x, y}
>>> (1 + x + 2*sin(y + I*pi)).atoms(Number) {1, 2}
>>> (1 + x + 2*sin(y + I*pi)).atoms(Number, NumberSymbol) {1, 2, pi}
>>> (1 + x + 2*sin(y + I*pi)).atoms(Number, NumberSymbol, I) {1, 2, I, pi}
Note that I (imaginary unit) and zoo (complex infinity) are special types of number symbols and are not part of the NumberSymbol class.
The type can be given implicitly, too:
>>> (1 + x + 2*sin(y + I*pi)).atoms(x) # x is a Symbol {x, y}
Be careful to check your assumptions when using the implicit option since
S(1).is_Integer = Truebuttype(S(1))isOne, a special type of SymPy atom, whiletype(S(2))is typeIntegerand will find all integers in an expression:>>> from sympy import S >>> (1 + x + 2*sin(y + I*pi)).atoms(S(1)) {1}
>>> (1 + x + 2*sin(y + I*pi)).atoms(S(2)) {1, 2}
Finally, arguments to atoms() can select more than atomic atoms: any SymPy type (loaded in core/__init__.py) can be listed as an argument and those types of “atoms” as found in scanning the arguments of the expression recursively:
>>> from sympy import Function, Mul >>> from sympy.core.function import AppliedUndef >>> f = Function('f') >>> (1 + f(x) + 2*sin(y + I*pi)).atoms(Function) {f(x), sin(y + I*pi)} >>> (1 + f(x) + 2*sin(y + I*pi)).atoms(AppliedUndef) {f(x)}
>>> (1 + x + 2*sin(y + I*pi)).atoms(Mul) {I*pi, 2*sin(y + I*pi)}
- property binary_symbols¶
Return from the atoms of self those which are free symbols.
Not all free symbols are
Symbol. Eg: IndexedBase(‘I’)[0].free_symbolsFor most expressions, all symbols are free symbols. For some classes this is not true. e.g. Integrals use Symbols for the dummy variables which are bound variables, so Integral has a method to return all symbols except those. Derivative keeps track of symbols with respect to which it will perform a derivative; those are bound variables, too, so it has its own free_symbols method.
Any other method that uses bound variables should implement a free_symbols method.
- cancel(*gens, **args)¶
See the cancel function in sympy.polys
- property canonical_variables¶
Return a dictionary mapping any variable defined in
self.bound_symbolsto Symbols that do not clash with any free symbols in the expression.Examples
>>> from sympy import Lambda >>> from sympy.abc import x >>> Lambda(x, 2*x).canonical_variables {x: _0}
- classmethod class_key()¶
Nice order of classes.
- coeff(x, n=1, right=False, _first=True)¶
Returns the coefficient from the term(s) containing
x**n. Ifnis zero then all terms independent ofxwill be returned.See also
as_coefficientseparate the expression into a coefficient and factor
as_coeff_Addseparate the additive constant from an expression
as_coeff_Mulseparate the multiplicative constant from an expression
as_independentseparate x-dependent terms/factors from others
sympy.polys.polytools.Poly.coeff_monomialefficiently find the single coefficient of a monomial in Poly
sympy.polys.polytools.Poly.nthlike coeff_monomial but powers of monomial terms are used
Examples
>>> from sympy import symbols >>> from sympy.abc import x, y, z
You can select terms that have an explicit negative in front of them:
>>> (-x + 2*y).coeff(-1) x >>> (x - 2*y).coeff(-1) 2*y
You can select terms with no Rational coefficient:
>>> (x + 2*y).coeff(1) x >>> (3 + 2*x + 4*x**2).coeff(1) 0
You can select terms independent of x by making n=0; in this case expr.as_independent(x)[0] is returned (and 0 will be returned instead of None):
>>> (3 + 2*x + 4*x**2).coeff(x, 0) 3 >>> eq = ((x + 1)**3).expand() + 1 >>> eq x**3 + 3*x**2 + 3*x + 2 >>> [eq.coeff(x, i) for i in reversed(range(4))] [1, 3, 3, 2] >>> eq -= 2 >>> [eq.coeff(x, i) for i in reversed(range(4))] [1, 3, 3, 0]
You can select terms that have a numerical term in front of them:
>>> (-x - 2*y).coeff(2) -y >>> from sympy import sqrt >>> (x + sqrt(2)*x).coeff(sqrt(2)) x
The matching is exact:
>>> (3 + 2*x + 4*x**2).coeff(x) 2 >>> (3 + 2*x + 4*x**2).coeff(x**2) 4 >>> (3 + 2*x + 4*x**2).coeff(x**3) 0 >>> (z*(x + y)**2).coeff((x + y)**2) z >>> (z*(x + y)**2).coeff(x + y) 0
In addition, no factoring is done, so 1 + z*(1 + y) is not obtained from the following:
>>> (x + z*(x + x*y)).coeff(x) 1
If such factoring is desired, factor_terms can be used first:
>>> from sympy import factor_terms >>> factor_terms(x + z*(x + x*y)).coeff(x) z*(y + 1) + 1
>>> n, m, o = symbols('n m o', commutative=False) >>> n.coeff(n) 1 >>> (3*n).coeff(n) 3 >>> (n*m + m*n*m).coeff(n) # = (1 + m)*n*m 1 + m >>> (n*m + m*n*m).coeff(n, right=True) # = (1 + m)*n*m m
If there is more than one possible coefficient 0 is returned:
>>> (n*m + m*n).coeff(n) 0
If there is only one possible coefficient, it is returned:
>>> (n*m + x*m*n).coeff(m*n) x >>> (n*m + x*m*n).coeff(m*n, right=1) 1
- collect(syms, func=None, evaluate=True, exact=False, distribute_order_term=True)¶
See the collect function in sympy.simplify
- combsimp()¶
See the combsimp function in sympy.simplify
- compare(other)¶
Return -1, 0, 1 if the object is smaller, equal, or greater than other.
Not in the mathematical sense. If the object is of a different type from the “other” then their classes are ordered according to the sorted_classes list.
Examples
>>> from sympy.abc import x, y >>> x.compare(y) -1 >>> x.compare(x) 0 >>> y.compare(x) 1
- compute_leading_term(x, logx=None)¶
Deprecated function to compute the leading term of a series.
as_leading_term is only allowed for results of .series() This is a wrapper to compute a series first.
- conjugate()¶
Returns the complex conjugate of ‘self’.
- copy()¶
- could_extract_minus_sign()¶
Return True if self has -1 as a leading factor or has more literal negative signs than positive signs in a sum, otherwise False.
Examples
>>> from sympy.abc import x, y >>> e = x - y >>> {i.could_extract_minus_sign() for i in (e, -e)} {False, True}
Though the
y - xis considered like-(x - y), since it is in a product without a leading factor of -1, the result is false below:>>> (x*(y - x)).could_extract_minus_sign() False
To put something in canonical form wrt to sign, use signsimp:
>>> from sympy import signsimp >>> signsimp(x*(y - x)) -x*(x - y) >>> _.could_extract_minus_sign() True
- count(query)¶
Count the number of matching subexpressions.
- count_ops(visual=None)¶
Wrapper for count_ops that returns the operation count.
- default_assumptions = {}¶
- diff(*symbols, **assumptions)¶
- dir(x, cdir)¶
- doit(**hints)¶
Evaluate objects that are not evaluated by default like limits, integrals, sums and products. All objects of this kind will be evaluated recursively, unless some species were excluded via ‘hints’ or unless the ‘deep’ hint was set to ‘False’.
>>> from sympy import Integral >>> from sympy.abc import x
>>> 2*Integral(x, x) 2*Integral(x, x)
>>> (2*Integral(x, x)).doit() x**2
>>> (2*Integral(x, x)).doit(deep=False) 2*Integral(x, x)
- dummy_eq(other, symbol=None)¶
Compare two expressions and handle dummy symbols.
Examples
>>> from sympy import Dummy >>> from sympy.abc import x, y
>>> u = Dummy('u')
>>> (u**2 + 1).dummy_eq(x**2 + 1) True >>> (u**2 + 1) == (x**2 + 1) False
>>> (u**2 + y).dummy_eq(x**2 + y, x) True >>> (u**2 + y).dummy_eq(x**2 + y, y) False
- equals(other, failing_expression=False)¶
Return True if self == other, False if it does not, or None. If failing_expression is True then the expression which did not simplify to a 0 will be returned instead of None.
- evalf(n=15, subs=None, maxn=100, chop=False, strict=False, quad=None, verbose=False)¶
Evaluate the given formula to an accuracy of n digits.
- Parameters:
- subsdict, optional
Substitute numerical values for symbols, e.g.
subs={x:3, y:1+pi}. The substitutions must be given as a dictionary.- maxnint, optional
Allow a maximum temporary working precision of maxn digits.
- chopbool or number, optional
Specifies how to replace tiny real or imaginary parts in subresults by exact zeros.
When
Truethe chop value defaults to standard precision.Otherwise the chop value is used to determine the magnitude of “small” for purposes of chopping.
>>> from sympy import N >>> x = 1e-4 >>> N(x, chop=True) 0.000100000000000000 >>> N(x, chop=1e-5) 0.000100000000000000 >>> N(x, chop=1e-4) 0
- strictbool, optional
Raise
PrecisionExhaustedif any subresult fails to evaluate to full accuracy, given the available maxprec.- quadstr, optional
Choose algorithm for numerical quadrature. By default, tanh-sinh quadrature is used. For oscillatory integrals on an infinite interval, try
quad='osc'.- verbosebool, optional
Print debug information.
Notes
When Floats are naively substituted into an expression, precision errors may adversely affect the result. For example, adding 1e16 (a Float) to 1 will truncate to 1e16; if 1e16 is then subtracted, the result will be 0. That is exactly what happens in the following:
>>> from sympy.abc import x, y, z >>> values = {x: 1e16, y: 1, z: 1e16} >>> (x + y - z).subs(values) 0
Using the subs argument for evalf is the accurate way to evaluate such an expression:
>>> (x + y - z).evalf(subs=values) 1.00000000000000
- expand(deep=True, modulus=None, power_base=True, power_exp=True, mul=True, log=True, multinomial=True, basic=True, **hints)¶
Expand an expression using hints.
See the docstring of the expand() function in sympy.core.function for more information.
- property expr_free_symbols¶
Like
free_symbols, but returns the free symbols only if they are contained in an expression node.Examples
>>> from sympy.abc import x, y >>> (x + y).expr_free_symbols {x, y}
If the expression is contained in a non-expression object, do not return the free symbols. Compare:
>>> from sympy import Tuple >>> t = Tuple(x + y) >>> t.expr_free_symbols set() >>> t.free_symbols {x, y}
- extract_additively(c)¶
Return self - c if it’s possible to subtract c from self and make all matching coefficients move towards zero, else return None.
See also
Examples
>>> from sympy.abc import x, y >>> e = 2*x + 3 >>> e.extract_additively(x + 1) x + 2 >>> e.extract_additively(3*x) >>> e.extract_additively(4) >>> (y*(x + 1)).extract_additively(x + 1) >>> ((x + 1)*(x + 2*y + 1) + 3).extract_additively(x + 1) (x + 1)*(x + 2*y) + 3
- extract_branch_factor(allow_half=False)¶
Try to write self as
exp_polar(2*pi*I*n)*zin a nice way. Return (z, n).>>> from sympy import exp_polar, I, pi >>> from sympy.abc import x, y >>> exp_polar(I*pi).extract_branch_factor() (exp_polar(I*pi), 0) >>> exp_polar(2*I*pi).extract_branch_factor() (1, 1) >>> exp_polar(-pi*I).extract_branch_factor() (exp_polar(I*pi), -1) >>> exp_polar(3*pi*I + x).extract_branch_factor() (exp_polar(x + I*pi), 1) >>> (y*exp_polar(-5*pi*I)*exp_polar(3*pi*I + 2*pi*x)).extract_branch_factor() (y*exp_polar(2*pi*x), -1) >>> exp_polar(-I*pi/2).extract_branch_factor() (exp_polar(-I*pi/2), 0)
If allow_half is True, also extract exp_polar(I*pi):
>>> exp_polar(I*pi).extract_branch_factor(allow_half=True) (1, 1/2) >>> exp_polar(2*I*pi).extract_branch_factor(allow_half=True) (1, 1) >>> exp_polar(3*I*pi).extract_branch_factor(allow_half=True) (1, 3/2) >>> exp_polar(-I*pi).extract_branch_factor(allow_half=True) (1, -1/2)
- extract_multiplicatively(c)¶
Return None if it’s not possible to make self in the form c * something in a nice way, i.e. preserving the properties of arguments of self.
Examples
>>> from sympy import symbols, Rational
>>> x, y = symbols('x,y', real=True)
>>> ((x*y)**3).extract_multiplicatively(x**2 * y) x*y**2
>>> ((x*y)**3).extract_multiplicatively(x**4 * y)
>>> (2*x).extract_multiplicatively(2) x
>>> (2*x).extract_multiplicatively(3)
>>> (Rational(1, 2)*x).extract_multiplicatively(3) x/6
- factor(*gens, **args)¶
See the factor() function in sympy.polys.polytools
- find(query, group=False)¶
Find all subexpressions matching a query.
- property formula¶
Return a Formula with only terms=[self].
- fourier_series(limits=None)¶
Compute fourier sine/cosine series of self.
See the docstring of the
fourier_series()in sympy.series.fourier for more information.
- fps(x=None, x0=0, dir=1, hyper=True, order=4, rational=True, full=False)¶
Compute formal power power series of self.
See the docstring of the
fps()function in sympy.series.formal for more information.
- property free_symbols¶
Return from the atoms of self those which are free symbols.
Not all free symbols are
Symbol. Eg: IndexedBase(‘I’)[0].free_symbolsFor most expressions, all symbols are free symbols. For some classes this is not true. e.g. Integrals use Symbols for the dummy variables which are bound variables, so Integral has a method to return all symbols except those. Derivative keeps track of symbols with respect to which it will perform a derivative; those are bound variables, too, so it has its own free_symbols method.
Any other method that uses bound variables should implement a free_symbols method.
- classmethod fromiter(args, **assumptions)¶
Create a new object from an iterable.
This is a convenience function that allows one to create objects from any iterable, without having to convert to a list or tuple first.
Examples
>>> from sympy import Tuple >>> Tuple.fromiter(i for i in range(5)) (0, 1, 2, 3, 4)
- property func¶
The top-level function in an expression.
The following should hold for all objects:
>> x == x.func(*x.args)
Examples
>>> from sympy.abc import x >>> a = 2*x >>> a.func <class 'sympy.core.mul.Mul'> >>> a.args (2, x) >>> a.func(*a.args) 2*x >>> a == a.func(*a.args) True
- gammasimp()¶
See the gammasimp function in sympy.simplify
- getO()¶
Returns the additive O(..) symbol if there is one, else None.
- getn()¶
Returns the order of the expression.
Examples
>>> from sympy import O >>> from sympy.abc import x >>> (1 + x + O(x**2)).getn() 2 >>> (1 + x).getn()
- has(*patterns)¶
Test whether any subexpression matches any of the patterns.
Examples
>>> from sympy import sin >>> from sympy.abc import x, y, z >>> (x**2 + sin(x*y)).has(z) False >>> (x**2 + sin(x*y)).has(x, y, z) True >>> x.has(x) True
Note
hasis a structural algorithm with no knowledge of mathematics. Consider the following half-open interval:>>> from sympy import Interval >>> i = Interval.Lopen(0, 5); i Interval.Lopen(0, 5) >>> i.args (0, 5, True, False) >>> i.has(4) # there is no "4" in the arguments False >>> i.has(0) # there *is* a "0" in the arguments True
Instead, use
containsto determine whether a number is in the interval or not:>>> i.contains(4) True >>> i.contains(0) False
Note that
expr.has(*patterns)is exactly equivalent toany(expr.has(p) for p in patterns). In particular,Falseis returned when the list of patterns is empty.>>> x.has() False
- has_free(*patterns)¶
Return True if self has object(s)
xas a free expression else False.Examples
>>> from sympy import Integral, Function >>> from sympy.abc import x, y >>> f = Function('f') >>> g = Function('g') >>> expr = Integral(f(x), (f(x), 1, g(y))) >>> expr.free_symbols {y} >>> expr.has_free(g(y)) True >>> expr.has_free(*(x, f(x))) False
This works for subexpressions and types, too:
>>> expr.has_free(g) True >>> (x + y + 1).has_free(y + 1) True
- has_xfree(s: set[Basic])¶
Return True if self has any of the patterns in s as a free argument, else False. This is like Basic.has_free but this will only report exact argument matches.
Examples
>>> from sympy import Function >>> from sympy.abc import x, y >>> f = Function('f') >>> f(x).has_xfree({f}) False >>> f(x).has_xfree({f(x)}) True >>> f(x + 1).has_xfree({x}) True >>> f(x + 1).has_xfree({x + 1}) True >>> f(x + y + 1).has_xfree({x + 1}) False
- integrate(*args, **kwargs)¶
See the integrate function in sympy.integrals
- invert(g, *gens, **args)¶
Return the multiplicative inverse of
selfmodgwhereself(andg) may be symbolic expressions).See also
sympy.core.numbers.mod_inverse,sympy.polys.polytools.invert
- is_Add = False¶
- is_AlgebraicNumber = False¶
- is_Atom = True¶
- is_Boolean = False¶
- is_Derivative = False¶
- is_Dummy = False¶
- is_Equality = False¶
- is_Float = False¶
- is_Function = False¶
- is_Indexed = False¶
- is_Integer = False¶
- is_MatAdd = False¶
- is_MatMul = False¶
- is_Matrix = False¶
- is_Mul = False¶
- is_Not = False¶
- is_Number = False¶
- is_NumberSymbol = False¶
- is_Order = False¶
- is_Piecewise = False¶
- is_Point = False¶
- is_Poly = False¶
- is_Pow = False¶
- is_Rational = False¶
- is_Relational = False¶
- is_Symbol = True¶
- is_Vector = False¶
- is_Wild = False¶
- property is_algebraic¶
- is_algebraic_expr(*syms)¶
This tests whether a given expression is algebraic or not, in the given symbols, syms. When syms is not given, all free symbols will be used. The rational function does not have to be in expanded or in any kind of canonical form.
This function returns False for expressions that are “algebraic expressions” with symbolic exponents. This is a simple extension to the is_rational_function, including rational exponentiation.
See also
References
Examples
>>> from sympy import Symbol, sqrt >>> x = Symbol('x', real=True) >>> sqrt(1 + x).is_rational_function() False >>> sqrt(1 + x).is_algebraic_expr() True
This function does not attempt any nontrivial simplifications that may result in an expression that does not appear to be an algebraic expression to become one.
>>> from sympy import exp, factor >>> a = sqrt(exp(x)**2 + 2*exp(x) + 1)/(exp(x) + 1) >>> a.is_algebraic_expr(x) False >>> factor(a).is_algebraic_expr() True
- property is_antihermitian¶
- property is_commutative¶
- is_comparable = False¶
- property is_complex¶
- property is_composite¶
- is_constant(*wrt, **flags)¶
Return True if self is constant, False if not, or None if the constancy could not be determined conclusively.
Examples
>>> from sympy import cos, sin, Sum, S, pi >>> from sympy.abc import a, n, x, y >>> x.is_constant() False >>> S(2).is_constant() True >>> Sum(x, (x, 1, 10)).is_constant() True >>> Sum(x, (x, 1, n)).is_constant() False >>> Sum(x, (x, 1, n)).is_constant(y) True >>> Sum(x, (x, 1, n)).is_constant(n) False >>> Sum(x, (x, 1, n)).is_constant(x) True >>> eq = a*cos(x)**2 + a*sin(x)**2 - a >>> eq.is_constant() True >>> eq.subs({x: pi, a: 2}) == eq.subs({x: pi, a: 3}) == 0 True
>>> (0**x).is_constant() False >>> x.is_constant() False >>> (x**x).is_constant() False >>> one = cos(x)**2 + sin(x)**2 >>> one.is_constant() True >>> ((one - 1)**(x + 1)).is_constant() in (True, False) # could be 0 or 1 True
- property is_even¶
- property is_extended_negative¶
- property is_extended_nonnegative¶
- property is_extended_nonpositive¶
- property is_extended_nonzero¶
- property is_extended_positive¶
- property is_extended_real¶
- property is_finite¶
- property is_hermitian¶
- is_hypergeometric(k)¶
- property is_imaginary¶
- property is_infinite¶
- property is_integer¶
- property is_irrational¶
- is_meromorphic(x, a)¶
This tests whether an expression is meromorphic as a function of the given symbol
xat the pointa.This method is intended as a quick test that will return None if no decision can be made without simplification or more detailed analysis.
Examples
>>> from sympy import zoo, log, sin, sqrt >>> from sympy.abc import x
>>> f = 1/x**2 + 1 - 2*x**3 >>> f.is_meromorphic(x, 0) True >>> f.is_meromorphic(x, 1) True >>> f.is_meromorphic(x, zoo) True
>>> g = x**log(3) >>> g.is_meromorphic(x, 0) False >>> g.is_meromorphic(x, 1) True >>> g.is_meromorphic(x, zoo) False
>>> h = sin(1/x)*x**2 >>> h.is_meromorphic(x, 0) False >>> h.is_meromorphic(x, 1) True >>> h.is_meromorphic(x, zoo) True
Multivalued functions are considered meromorphic when their branches are meromorphic. Thus most functions are meromorphic everywhere except at essential singularities and branch points. In particular, they will be meromorphic also on branch cuts except at their endpoints.
>>> log(x).is_meromorphic(x, -1) True >>> log(x).is_meromorphic(x, 0) False >>> sqrt(x).is_meromorphic(x, -1) True >>> sqrt(x).is_meromorphic(x, 0) False
- property is_negative¶
- property is_noninteger¶
- property is_nonnegative¶
- property is_nonpositive¶
- property is_nonzero¶
- is_number = False¶
- property is_odd¶
- property is_polar¶
- is_polynomial(*syms)¶
Return True if self is a polynomial in syms and False otherwise.
This checks if self is an exact polynomial in syms. This function returns False for expressions that are “polynomials” with symbolic exponents. Thus, you should be able to apply polynomial algorithms to expressions for which this returns True, and Poly(expr, *syms) should work if and only if expr.is_polynomial(*syms) returns True. The polynomial does not have to be in expanded form. If no symbols are given, all free symbols in the expression will be used.
This is not part of the assumptions system. You cannot do Symbol(‘z’, polynomial=True).
Examples
>>> from sympy import Symbol, Function >>> x = Symbol('x') >>> ((x**2 + 1)**4).is_polynomial(x) True >>> ((x**2 + 1)**4).is_polynomial() True >>> (2**x + 1).is_polynomial(x) False >>> (2**x + 1).is_polynomial(2**x) True >>> f = Function('f') >>> (f(x) + 1).is_polynomial(x) False >>> (f(x) + 1).is_polynomial(f(x)) True >>> (1/f(x) + 1).is_polynomial(f(x)) False
>>> n = Symbol('n', nonnegative=True, integer=True) >>> (x**n + 1).is_polynomial(x) False
This function does not attempt any nontrivial simplifications that may result in an expression that does not appear to be a polynomial to become one.
>>> from sympy import sqrt, factor, cancel >>> y = Symbol('y', positive=True) >>> a = sqrt(y**2 + 2*y + 1) >>> a.is_polynomial(y) False >>> factor(a) y + 1 >>> factor(a).is_polynomial(y) True
>>> b = (y**2 + 2*y + 1)/(y + 1) >>> b.is_polynomial(y) False >>> cancel(b) y + 1 >>> cancel(b).is_polynomial(y) True
See also .is_rational_function()
- property is_positive¶
- property is_prime¶
- property is_rational¶
- is_rational_function(*syms)¶
Test whether function is a ratio of two polynomials in the given symbols, syms. When syms is not given, all free symbols will be used. The rational function does not have to be in expanded or in any kind of canonical form.
This function returns False for expressions that are “rational functions” with symbolic exponents. Thus, you should be able to call .as_numer_denom() and apply polynomial algorithms to the result for expressions for which this returns True.
This is not part of the assumptions system. You cannot do Symbol(‘z’, rational_function=True).
Examples
>>> from sympy import Symbol, sin >>> from sympy.abc import x, y
>>> (x/y).is_rational_function() True
>>> (x**2).is_rational_function() True
>>> (x/sin(y)).is_rational_function(y) False
>>> n = Symbol('n', integer=True) >>> (x**n + 1).is_rational_function(x) False
This function does not attempt any nontrivial simplifications that may result in an expression that does not appear to be a rational function to become one.
>>> from sympy import sqrt, factor >>> y = Symbol('y', positive=True) >>> a = sqrt(y**2 + 2*y + 1)/y >>> a.is_rational_function(y) False >>> factor(a) (y + 1)/y >>> factor(a).is_rational_function(y) True
See also is_algebraic_expr().
- property is_real¶
- is_scalar = True¶
- is_symbol = True¶
- property is_transcendental¶
- property is_zero¶
- property kind¶
Default kind for all SymPy object. If the kind is not defined for the object, or if the object cannot infer the kind from its arguments, this will be returned.
Examples
>>> from sympy import Expr >>> Expr().kind UndefinedKind
- leadterm(x, logx=None, cdir=0)¶
Returns the leading term a*x**b as a tuple (a, b).
Examples
>>> from sympy.abc import x >>> (1+x+x**2).leadterm(x) (1, 0) >>> (1/x**2+x+x**2).leadterm(x) (1, -2)
- limit(x, xlim, dir='+')¶
Compute limit x->xlim.
- lseries(x=None, x0=0, dir='+', logx=None, cdir=0)¶
Wrapper for series yielding an iterator of the terms of the series.
Note: an infinite series will yield an infinite iterator. The following, for exaxmple, will never terminate. It will just keep printing terms of the sin(x) series:
for term in sin(x).lseries(x): print term
The advantage of lseries() over nseries() is that many times you are just interested in the next term in the series (i.e. the first term for example), but you do not know how many you should ask for in nseries() using the “n” parameter.
See also nseries().
- match(pattern, old=False)¶
Pattern matching.
Wild symbols match all.
Return
Nonewhen expression (self) does not match with pattern. Otherwise return a dictionary such that:pattern.xreplace(self.match(pattern)) == self
Examples
>>> from sympy import Wild, Sum >>> from sympy.abc import x, y >>> p = Wild("p") >>> q = Wild("q") >>> r = Wild("r") >>> e = (x+y)**(x+y) >>> e.match(p**p) {p_: x + y} >>> e.match(p**q) {p_: x + y, q_: x + y} >>> e = (2*x)**2 >>> e.match(p*q**r) {p_: 4, q_: x, r_: 2} >>> (p*q**r).xreplace(e.match(p*q**r)) 4*x**2
Structurally bound symbols are ignored during matching:
>>> Sum(x, (x, 1, 2)).match(Sum(y, (y, 1, p))) {p_: 2}
But they can be identified if desired:
>>> Sum(x, (x, 1, 2)).match(Sum(q, (q, 1, p))) {p_: 2, q_: x}
The
oldflag will give the old-style pattern matching where expressions and patterns are essentially solved to give the match. Both of the following give None unlessold=True:>>> (x - 2).match(p - x, old=True) {p_: 2*x - 2} >>> (2/x).match(p*x, old=True) {p_: 2/x**2}
- matches(expr, repl_dict=None, old=False)¶
Helper method for match() that looks for a match between Wild symbols in self and expressions in expr.
Examples
>>> from sympy import symbols, Wild, Basic >>> a, b, c = symbols('a b c') >>> x = Wild('x') >>> Basic(a + x, x).matches(Basic(a + b, c)) is None True >>> Basic(a + x, x).matches(Basic(a + b + c, b + c)) {x_: b + c}
- n(n=15, subs=None, maxn=100, chop=False, strict=False, quad=None, verbose=False)¶
Evaluate the given formula to an accuracy of n digits.
- Parameters:
- subsdict, optional
Substitute numerical values for symbols, e.g.
subs={x:3, y:1+pi}. The substitutions must be given as a dictionary.- maxnint, optional
Allow a maximum temporary working precision of maxn digits.
- chopbool or number, optional
Specifies how to replace tiny real or imaginary parts in subresults by exact zeros.
When
Truethe chop value defaults to standard precision.Otherwise the chop value is used to determine the magnitude of “small” for purposes of chopping.
>>> from sympy import N >>> x = 1e-4 >>> N(x, chop=True) 0.000100000000000000 >>> N(x, chop=1e-5) 0.000100000000000000 >>> N(x, chop=1e-4) 0
- strictbool, optional
Raise
PrecisionExhaustedif any subresult fails to evaluate to full accuracy, given the available maxprec.- quadstr, optional
Choose algorithm for numerical quadrature. By default, tanh-sinh quadrature is used. For oscillatory integrals on an infinite interval, try
quad='osc'.- verbosebool, optional
Print debug information.
Notes
When Floats are naively substituted into an expression, precision errors may adversely affect the result. For example, adding 1e16 (a Float) to 1 will truncate to 1e16; if 1e16 is then subtracted, the result will be 0. That is exactly what happens in the following:
>>> from sympy.abc import x, y, z >>> values = {x: 1e16, y: 1, z: 1e16} >>> (x + y - z).subs(values) 0
Using the subs argument for evalf is the accurate way to evaluate such an expression:
>>> (x + y - z).evalf(subs=values) 1.00000000000000
- name: str¶
- normal()¶
Return the expression as a fraction.
expression -> a/b
See also
as_numer_denomreturn
(a, b)instead ofa/b
- nseries(x=None, x0=0, n=6, dir='+', logx=None, cdir=0)¶
Wrapper to _eval_nseries if assumptions allow, else to series.
If x is given, x0 is 0, dir=’+’, and self has x, then _eval_nseries is called. This calculates “n” terms in the innermost expressions and then builds up the final series just by “cross-multiplying” everything out.
The optional
logxparameter can be used to replace any log(x) in the returned series with a symbolic value to avoid evaluating log(x) at 0. A symbol to use in place of log(x) should be provided.Advantage – it’s fast, because we do not have to determine how many terms we need to calculate in advance.
Disadvantage – you may end up with less terms than you may have expected, but the O(x**n) term appended will always be correct and so the result, though perhaps shorter, will also be correct.
If any of those assumptions is not met, this is treated like a wrapper to series which will try harder to return the correct number of terms.
See also lseries().
Examples
>>> from sympy import sin, log, Symbol >>> from sympy.abc import x, y >>> sin(x).nseries(x, 0, 6) x - x**3/6 + x**5/120 + O(x**6) >>> log(x+1).nseries(x, 0, 5) x - x**2/2 + x**3/3 - x**4/4 + O(x**5)
Handling of the
logxparameter — in the following example the expansion fails sincesindoes not have an asymptotic expansion at -oo (the limit of log(x) as x approaches 0):>>> e = sin(log(x)) >>> e.nseries(x, 0, 6) Traceback (most recent call last): ... PoleError: ... ... >>> logx = Symbol('logx') >>> e.nseries(x, 0, 6, logx=logx) sin(logx)
In the following example, the expansion works but only returns self unless the
logxparameter is used:>>> e = x**y >>> e.nseries(x, 0, 2) x**y >>> e.nseries(x, 0, 2, logx=logx) exp(logx*y)
- nsimplify(constants=(), tolerance=None, full=False)¶
See the nsimplify function in sympy.simplify
- powsimp(*args, **kwargs)¶
See the powsimp function in sympy.simplify
- primitive()¶
Return the positive Rational that can be extracted non-recursively from every term of self (i.e., self is treated like an Add). This is like the as_coeff_Mul() method but primitive always extracts a positive Rational (never a negative or a Float).
Examples
>>> from sympy.abc import x >>> (3*(x + 1)**2).primitive() (3, (x + 1)**2) >>> a = (6*x + 2); a.primitive() (2, 3*x + 1) >>> b = (x/2 + 3); b.primitive() (1/2, x + 6) >>> (a*b).primitive() == (1, a*b) True
- radsimp(**kwargs)¶
See the radsimp function in sympy.simplify
- ratsimp()¶
See the ratsimp function in sympy.simplify
- rcall(*args)¶
Apply on the argument recursively through the expression tree.
This method is used to simulate a common abuse of notation for operators. For instance, in SymPy the following will not work:
(x+Lambda(y, 2*y))(z) == x+2*z,however, you can use:
>>> from sympy import Lambda >>> from sympy.abc import x, y, z >>> (x + Lambda(y, 2*y)).rcall(z) x + 2*z
- refine(assumption=True)¶
See the refine function in sympy.assumptions
- removeO()¶
Removes the additive O(..) symbol if there is one
- replace(query, value, map=False, simultaneous=True, exact=None)¶
Replace matching subexpressions of
selfwithvalue.If
map = Truethen also return the mapping {old: new} whereoldwas a sub-expression found with query andnewis the replacement value for it. If the expression itself does not match the query, then the returned value will beself.xreplace(map)otherwise it should beself.subs(ordered(map.items())).Traverses an expression tree and performs replacement of matching subexpressions from the bottom to the top of the tree. The default approach is to do the replacement in a simultaneous fashion so changes made are targeted only once. If this is not desired or causes problems,
simultaneouscan be set to False.In addition, if an expression containing more than one Wild symbol is being used to match subexpressions and the
exactflag is None it will be set to True so the match will only succeed if all non-zero values are received for each Wild that appears in the match pattern. Setting this to False accepts a match of 0; while setting it True accepts all matches that have a 0 in them. See example below for cautions.The list of possible combinations of queries and replacement values is listed below:
See also
Examples
Initial setup
>>> from sympy import log, sin, cos, tan, Wild, Mul, Add >>> from sympy.abc import x, y >>> f = log(sin(x)) + tan(sin(x**2))
- 1.1. type -> type
obj.replace(type, newtype)
When object of type
typeis found, replace it with the result of passing its argument(s) tonewtype.>>> f.replace(sin, cos) log(cos(x)) + tan(cos(x**2)) >>> sin(x).replace(sin, cos, map=True) (cos(x), {sin(x): cos(x)}) >>> (x*y).replace(Mul, Add) x + y
- 1.2. type -> func
obj.replace(type, func)
When object of type
typeis found, applyfuncto its argument(s).funcmust be written to handle the number of arguments oftype.>>> f.replace(sin, lambda arg: sin(2*arg)) log(sin(2*x)) + tan(sin(2*x**2)) >>> (x*y).replace(Mul, lambda *args: sin(2*Mul(*args))) sin(2*x*y)
- 2.1. pattern -> expr
obj.replace(pattern(wild), expr(wild))
Replace subexpressions matching
patternwith the expression written in terms of the Wild symbols inpattern.>>> a, b = map(Wild, 'ab') >>> f.replace(sin(a), tan(a)) log(tan(x)) + tan(tan(x**2)) >>> f.replace(sin(a), tan(a/2)) log(tan(x/2)) + tan(tan(x**2/2)) >>> f.replace(sin(a), a) log(x) + tan(x**2) >>> (x*y).replace(a*x, a) y
Matching is exact by default when more than one Wild symbol is used: matching fails unless the match gives non-zero values for all Wild symbols:
>>> (2*x + y).replace(a*x + b, b - a) y - 2 >>> (2*x).replace(a*x + b, b - a) 2*x
When set to False, the results may be non-intuitive:
>>> (2*x).replace(a*x + b, b - a, exact=False) 2/x
- 2.2. pattern -> func
obj.replace(pattern(wild), lambda wild: expr(wild))
All behavior is the same as in 2.1 but now a function in terms of pattern variables is used rather than an expression:
>>> f.replace(sin(a), lambda a: sin(2*a)) log(sin(2*x)) + tan(sin(2*x**2))
- 3.1. func -> func
obj.replace(filter, func)
Replace subexpression
ewithfunc(e)iffilter(e)is True.>>> g = 2*sin(x**3) >>> g.replace(lambda expr: expr.is_Number, lambda expr: expr**2) 4*sin(x**9)
The expression itself is also targeted by the query but is done in such a fashion that changes are not made twice.
>>> e = x*(x*y + 1) >>> e.replace(lambda x: x.is_Mul, lambda x: 2*x) 2*x*(2*x*y + 1)
When matching a single symbol, exact will default to True, but this may or may not be the behavior that is desired:
Here, we want exact=False:
>>> from sympy import Function >>> f = Function('f') >>> e = f(1) + f(0) >>> q = f(a), lambda a: f(a + 1) >>> e.replace(*q, exact=False) f(1) + f(2) >>> e.replace(*q, exact=True) f(0) + f(2)
But here, the nature of matching makes selecting the right setting tricky:
>>> e = x**(1 + y) >>> (x**(1 + y)).replace(x**(1 + a), lambda a: x**-a, exact=False) x >>> (x**(1 + y)).replace(x**(1 + a), lambda a: x**-a, exact=True) x**(-x - y + 1) >>> (x**y).replace(x**(1 + a), lambda a: x**-a, exact=False) x >>> (x**y).replace(x**(1 + a), lambda a: x**-a, exact=True) x**(1 - y)
It is probably better to use a different form of the query that describes the target expression more precisely:
>>> (1 + x**(1 + y)).replace( ... lambda x: x.is_Pow and x.exp.is_Add and x.exp.args[0] == 1, ... lambda x: x.base**(1 - (x.exp - 1))) ... x**(1 - y) + 1
- rewrite(*args, deep=True, **hints)¶
Rewrite self using a defined rule.
Rewriting transforms an expression to another, which is mathematically equivalent but structurally different. For example you can rewrite trigonometric functions as complex exponentials or combinatorial functions as gamma function.
This method takes a pattern and a rule as positional arguments. pattern is optional parameter which defines the types of expressions that will be transformed. If it is not passed, all possible expressions will be rewritten. rule defines how the expression will be rewritten.
- Parameters:
- argsExpr
A rule, or pattern and rule. - pattern is a type or an iterable of types. - rule can be any object.
- deepbool, optional
If
True, subexpressions are recursively transformed. Default isTrue.
Examples
If pattern is unspecified, all possible expressions are transformed.
>>> from sympy import cos, sin, exp, I >>> from sympy.abc import x >>> expr = cos(x) + I*sin(x) >>> expr.rewrite(exp) exp(I*x)
Pattern can be a type or an iterable of types.
>>> expr.rewrite(sin, exp) exp(I*x)/2 + cos(x) - exp(-I*x)/2 >>> expr.rewrite([cos,], exp) exp(I*x)/2 + I*sin(x) + exp(-I*x)/2 >>> expr.rewrite([cos, sin], exp) exp(I*x)
Rewriting behavior can be implemented by defining
_eval_rewrite()method.>>> from sympy import Expr, sqrt, pi >>> class MySin(Expr): ... def _eval_rewrite(self, rule, args, **hints): ... x, = args ... if rule == cos: ... return cos(pi/2 - x, evaluate=False) ... if rule == sqrt: ... return sqrt(1 - cos(x)**2) >>> MySin(MySin(x)).rewrite(cos) cos(-cos(-x + pi/2) + pi/2) >>> MySin(x).rewrite(sqrt) sqrt(1 - cos(x)**2)
Defining
_eval_rewrite_as_[...]()method is supported for backwards compatibility reason. This may be removed in the future and using it is discouraged.>>> class MySin(Expr): ... def _eval_rewrite_as_cos(self, *args, **hints): ... x, = args ... return cos(pi/2 - x, evaluate=False) >>> MySin(x).rewrite(cos) cos(-x + pi/2)
- round(n=None)¶
Return x rounded to the given decimal place.
If a complex number would results, apply round to the real and imaginary components of the number.
Notes
The Python
roundfunction uses the SymPyroundmethod so it will always return a SymPy number (not a Python float or int):>>> isinstance(round(S(123), -2), Number) True
Examples
>>> from sympy import pi, E, I, S, Number >>> pi.round() 3 >>> pi.round(2) 3.14 >>> (2*pi + E*I).round() 6 + 3*I
The round method has a chopping effect:
>>> (2*pi + I/10).round() 6 >>> (pi/10 + 2*I).round() 2*I >>> (pi/10 + E*I).round(2) 0.31 + 2.72*I
- separate(deep=False, force=False)¶
See the separate function in sympy.simplify
- series(x=None, x0=0, n=6, dir='+', logx=None, cdir=0)¶
Series expansion of “self” around
x = x0yielding either terms of the series one by one (the lazy series given when n=None), else all the terms at once when n != None.Returns the series expansion of “self” around the point
x = x0with respect toxup toO((x - x0)**n, x, x0)(default n is 6).If
x=Noneandselfis univariate, the univariate symbol will be supplied, otherwise an error will be raised.- Parameters:
- exprExpression
The expression whose series is to be expanded.
- xSymbol
It is the variable of the expression to be calculated.
- x0Value
The value around which
xis calculated. Can be any value from-ootooo.- nValue
The value used to represent the order in terms of
x**n, up to which the series is to be expanded.- dirString, optional
The series-expansion can be bi-directional. If
dir="+", then (x->x0+). Ifdir="-", then (x->x0-). For infinite ``x0(ooor-oo), thedirargument is determined from the direction of the infinity (i.e.,dir="-"foroo).- logxoptional
It is used to replace any log(x) in the returned series with a symbolic value rather than evaluating the actual value.
- cdiroptional
It stands for complex direction, and indicates the direction from which the expansion needs to be evaluated.
- Returns:
- ExprExpression
Series expansion of the expression about x0
- Raises:
- TypeError
If “n” and “x0” are infinity objects
- PoleError
If “x0” is an infinity object
Examples
>>> from sympy import cos, exp, tan >>> from sympy.abc import x, y >>> cos(x).series() 1 - x**2/2 + x**4/24 + O(x**6) >>> cos(x).series(n=4) 1 - x**2/2 + O(x**4) >>> cos(x).series(x, x0=1, n=2) cos(1) - (x - 1)*sin(1) + O((x - 1)**2, (x, 1)) >>> e = cos(x + exp(y)) >>> e.series(y, n=2) cos(x + 1) - y*sin(x + 1) + O(y**2) >>> e.series(x, n=2) cos(exp(y)) - x*sin(exp(y)) + O(x**2)
If
n=Nonethen a generator of the series terms will be returned.>>> term=cos(x).series(n=None) >>> [next(term) for i in range(2)] [1, -x**2/2]
For
dir=+(default) the series is calculated from the right and fordir=-the series from the left. For smooth functions this flag will not alter the results.>>> abs(x).series(dir="+") x >>> abs(x).series(dir="-") -x >>> f = tan(x) >>> f.series(x, 2, 6, "+") tan(2) + (1 + tan(2)**2)*(x - 2) + (x - 2)**2*(tan(2)**3 + tan(2)) + (x - 2)**3*(1/3 + 4*tan(2)**2/3 + tan(2)**4) + (x - 2)**4*(tan(2)**5 + 5*tan(2)**3/3 + 2*tan(2)/3) + (x - 2)**5*(2/15 + 17*tan(2)**2/15 + 2*tan(2)**4 + tan(2)**6) + O((x - 2)**6, (x, 2))
>>> f.series(x, 2, 3, "-") tan(2) + (2 - x)*(-tan(2)**2 - 1) + (2 - x)**2*(tan(2)**3 + tan(2)) + O((x - 2)**3, (x, 2))
For rational expressions this method may return original expression without the Order term. >>> (1/x).series(x, n=8) 1/x
- simplify(**kwargs)¶
See the simplify function in sympy.simplify
- sort_key(order=None)¶
Return a sort key.
Examples
>>> from sympy import S, I
>>> sorted([S(1)/2, I, -I], key=lambda x: x.sort_key()) [1/2, -I, I]
>>> S("[x, 1/x, 1/x**2, x**2, x**(1/2), x**(1/4), x**(3/2)]") [x, 1/x, x**(-2), x**2, sqrt(x), x**(1/4), x**(3/2)] >>> sorted(_, key=lambda x: x.sort_key()) [x**(-2), 1/x, x**(1/4), sqrt(x), x, x**(3/2), x**2]
- subs(*args, **kwargs)¶
Substitutes old for new in an expression after sympifying args.
- args is either:
two arguments, e.g. foo.subs(old, new)
- one iterable argument, e.g. foo.subs(iterable). The iterable may be
- o an iterable container with (old, new) pairs. In this case the
replacements are processed in the order given with successive patterns possibly affecting replacements already made.
- o a dict or set whose key/value items correspond to old/new pairs.
In this case the old/new pairs will be sorted by op count and in case of a tie, by number of args and the default_sort_key. The resulting sorted list is then processed as an iterable container (see previous).
If the keyword
simultaneousis True, the subexpressions will not be evaluated until all the substitutions have been made.See also
Examples
>>> from sympy import pi, exp, limit, oo >>> from sympy.abc import x, y >>> (1 + x*y).subs(x, pi) pi*y + 1 >>> (1 + x*y).subs({x:pi, y:2}) 1 + 2*pi >>> (1 + x*y).subs([(x, pi), (y, 2)]) 1 + 2*pi >>> reps = [(y, x**2), (x, 2)] >>> (x + y).subs(reps) 6 >>> (x + y).subs(reversed(reps)) x**2 + 2
>>> (x**2 + x**4).subs(x**2, y) y**2 + y
To replace only the x**2 but not the x**4, use xreplace:
>>> (x**2 + x**4).xreplace({x**2: y}) x**4 + y
To delay evaluation until all substitutions have been made, set the keyword
simultaneousto True:>>> (x/y).subs([(x, 0), (y, 0)]) 0 >>> (x/y).subs([(x, 0), (y, 0)], simultaneous=True) nan
This has the added feature of not allowing subsequent substitutions to affect those already made:
>>> ((x + y)/y).subs({x + y: y, y: x + y}) 1 >>> ((x + y)/y).subs({x + y: y, y: x + y}, simultaneous=True) y/(x + y)
In order to obtain a canonical result, unordered iterables are sorted by count_op length, number of arguments and by the default_sort_key to break any ties. All other iterables are left unsorted.
>>> from sympy import sqrt, sin, cos >>> from sympy.abc import a, b, c, d, e
>>> A = (sqrt(sin(2*x)), a) >>> B = (sin(2*x), b) >>> C = (cos(2*x), c) >>> D = (x, d) >>> E = (exp(x), e)
>>> expr = sqrt(sin(2*x))*sin(exp(x)*x)*cos(2*x) + sin(2*x)
>>> expr.subs(dict([A, B, C, D, E])) a*c*sin(d*e) + b
The resulting expression represents a literal replacement of the old arguments with the new arguments. This may not reflect the limiting behavior of the expression:
>>> (x**3 - 3*x).subs({x: oo}) nan
>>> limit(x**3 - 3*x, x, oo) oo
If the substitution will be followed by numerical evaluation, it is better to pass the substitution to evalf as
>>> (1/x).evalf(subs={x: 3.0}, n=21) 0.333333333333333333333
rather than
>>> (1/x).subs({x: 3.0}).evalf(21) 0.333333333333333314830
as the former will ensure that the desired level of precision is obtained.
- taylor_term(n, x, *previous_terms)¶
General method for the taylor term.
This method is slow, because it differentiates n-times. Subclasses can redefine it to make it faster by using the “previous_terms”.
- to_nnf(simplify=True)¶
- together(*args, **kwargs)¶
See the together function in sympy.polys
- transpose()¶
- trigsimp(**args)¶
See the trigsimp function in sympy.simplify
- xreplace(rule, hack2=False)¶
Replace occurrences of objects within the expression.
- Parameters:
- ruledict-like
Expresses a replacement rule
- Returns:
- xreplacethe result of the replacement
See also
Examples
>>> from sympy import symbols, pi, exp >>> x, y, z = symbols('x y z') >>> (1 + x*y).xreplace({x: pi}) pi*y + 1 >>> (1 + x*y).xreplace({x: pi, y: 2}) 1 + 2*pi
Replacements occur only if an entire node in the expression tree is matched:
>>> (x*y + z).xreplace({x*y: pi}) z + pi >>> (x*y*z).xreplace({x*y: pi}) x*y*z >>> (2*x).xreplace({2*x: y, x: z}) y >>> (2*2*x).xreplace({2*x: y, x: z}) 4*z >>> (x + y + 2).xreplace({x + y: 2}) x + y + 2 >>> (x + 2 + exp(x + 2)).xreplace({x + 2: y}) x + exp(y) + 2
xreplace does not differentiate between free and bound symbols. In the following, subs(x, y) would not change x since it is a bound symbol, but xreplace does:
>>> from sympy import Integral >>> Integral(x, (x, 1, 2*x)).xreplace({x: y}) Integral(y, (y, 1, 2*y))
Trying to replace x with an expression raises an error:
>>> Integral(x, (x, 1, 2*x)).xreplace({x: 2*y}) ValueError: Invalid limits given: ((2*y, 1, 4*y),)
Functions¶
- nipy.algorithms.statistics.formula.formulae.contrast_from_cols_or_rows(L, D, pseudo=None)¶
Construct a contrast matrix from a design matrix D
(possibly with its pseudo inverse already computed) and a matrix L that either specifies something in the column space of D or the row space of D.
- Parameters:
- Lndarray
Matrix used to try and construct a contrast.
- Dndarray
Design matrix used to create the contrast.
- pseudoNone or array-like, optional
If not None, gives pseudo-inverse of D. Allows you to pass this if it is already calculated.
- Returns:
- Cndarray
Matrix with C.shape[1] == D.shape[1] representing an estimable contrast.
Notes
From an n x p design matrix D and a matrix L, tries to determine a p x q contrast matrix C which determines a contrast of full rank, i.e. the n x q matrix
dot(transpose(C), pinv(D))
is full rank.
L must satisfy either L.shape[0] == n or L.shape[1] == p.
If L.shape[0] == n, then L is thought of as representing columns in the column space of D.
If L.shape[1] == p, then L is thought of as what is known as a contrast matrix. In this case, this function returns an estimable contrast corresponding to the dot(D, L.T)
This always produces a meaningful contrast, not always with the intended properties because q is always non-zero unless L is identically 0. That is, it produces a contrast that spans the column space of L (after projection onto the column space of D).
- nipy.algorithms.statistics.formula.formulae.define(*args, **kwargs)¶
- nipy.algorithms.statistics.formula.formulae.getparams(expression)¶
Return the parameters of an expression that are not Term instances but are instances of sympy.Symbol.
Examples
>>> x, y, z = [Term(l) for l in 'xyz'] >>> f = Formula([x,y,z]) >>> getparams(f) [] >>> f.mean _b0*x + _b1*y + _b2*z >>> getparams(f.mean) [_b0, _b1, _b2] >>> th = sympy.Symbol('theta') >>> f.mean*sympy.exp(th) (_b0*x + _b1*y + _b2*z)*exp(theta) >>> getparams(f.mean*sympy.exp(th)) [_b0, _b1, _b2, theta]
- nipy.algorithms.statistics.formula.formulae.getterms(expression)¶
Return the all instances of Term in an expression.
Examples
>>> x, y, z = [Term(l) for l in 'xyz'] >>> f = Formula([x,y,z]) >>> getterms(f) [x, y, z] >>> getterms(f.mean) [x, y, z]
- nipy.algorithms.statistics.formula.formulae.is_factor(obj)¶
Is obj a Factor?
- nipy.algorithms.statistics.formula.formulae.is_factor_term(obj)¶
Is obj a FactorTerm?
- nipy.algorithms.statistics.formula.formulae.is_formula(obj)¶
Is obj a Formula?
- nipy.algorithms.statistics.formula.formulae.is_term(obj)¶
Is obj a Term?
- nipy.algorithms.statistics.formula.formulae.make_dummy(name)¶
make_dummy is deprecated! Please use sympy.Dummy instead of this function
Make dummy variable of given name
- Parameters:
- namestr
name of dummy variable
- Returns:
- dumDummy instance
Notes
The interface to Dummy changed between 0.6.7 and 0.7.0, and we used this function to keep compatibility. Now we depend on sympy 0.7.0 and this function is obsolete.
- nipy.algorithms.statistics.formula.formulae.make_recarray(rows, names, dtypes=None, drop_name_dim=<class 'nipy.utils._NoValue'>)¶
Create recarray from rows with field names names
Create a recarray with named columns from a list or ndarray of rows and sequence of names for the columns. If rows is an ndarray, dtypes must be None, otherwise we raise a ValueError. Otherwise, if dtypes is None, we cast the data in all columns in rows as np.float64. If dtypes is not None, the routine uses dtypes as a dtype specifier for the output structured array.
- Parameters:
- rows: list or array
Rows that will be turned into an recarray.
- names: sequence
Sequence of strings - names for the columns.
- dtypes: None or sequence of str or sequence of np.dtype, optional
Used to create a np.dtype, can be sequence of np.dtype or string.
- drop_name_dim{_NoValue, False, True}, optional
Flag for compatibility with future default behavior. Current default is False. If True, drops the length 1 dimension corresponding to the axis transformed into fields when converting into a recarray. If _NoValue specified, gives default. Default will change to True in the next version of Nipy.
- Returns:
- vnp.ndarray
Structured array with field names given by names.
- Raises:
- ValueError
dtypes not None when rows is array.
Examples
The following tests depend on machine byte order for their exact output.
>>> arr = np.array([[3, 4], [4, 6], [6, 8]]) >>> make_recarray(arr, ['x', 'y'], ... drop_name_dim=True) array([(3, 4), (4, 6), (6, 8)], dtype=[('x', '<i8'), ('y', '<i8')]) >>> make_recarray(arr, ['x', 'y'], ... drop_name_dim=False) array([[(3, 4)], [(4, 6)], [(6, 8)]], dtype=[('x', '<i8'), ('y', '<i8')]) >>> r = make_recarray(arr, ['w', 'u'], drop_name_dim=True) >>> make_recarray(r, ['x', 'y'], ... drop_name_dim=True) array([(3, 4), (4, 6), (6, 8)], dtype=[('x', '<i8'), ('y', '<i8')]) >>> make_recarray([[3, 4], [4, 6], [7, 9]], 'wv', ... [np.float64, np.int_]) array([(3.0, 4), (4.0, 6), (7.0, 9)], dtype=[('w', '<f8'), ('v', '<i8')])
- nipy.algorithms.statistics.formula.formulae.natural_spline(t, knots=None, order=3, intercept=False)¶
Return a Formula containing a natural spline
Spline for a Term with specified knots and order.
- Parameters:
- t
Term - knotsNone or sequence, optional
Sequence of float. Default None (same as empty list)
- orderint, optional
Order of the spline. Defaults to a cubic (==3)
- interceptbool, optional
If True, include a constant function in the natural spline. Default is False
- t
- Returns:
- formulaFormula
A Formula with (len(knots) + order) Terms (if intercept=False, otherwise includes one more Term), made up of the natural spline functions.
Examples
>>> x = Term('x') >>> n = natural_spline(x, knots=[1,3,4], order=3) >>> xval = np.array([3,5,7.]).view(np.dtype([('x', np.float64)])) >>> n.design(xval, return_float=True) array([[ 3., 9., 27., 8., 0., -0.], [ 5., 25., 125., 64., 8., 1.], [ 7., 49., 343., 216., 64., 27.]]) >>> d = n.design(xval) >>> print(d.dtype.descr) [('ns_1(x)', '<f8'), ('ns_2(x)', '<f8'), ('ns_3(x)', '<f8'), ('ns_4(x)', '<f8'), ('ns_5(x)', '<f8'), ('ns_6(x)', '<f8')]
- nipy.algorithms.statistics.formula.formulae.terms(names, **kwargs)¶
Return list of terms with names given by names
This is just a convenience in defining a set of terms, and is the equivalent of
sympy.symbolsfor defining symbols in sympy.We enforce the sympy 0.7.0 behavior of returning symbol “abc” from input “abc”, rthan than 3 symbols “a”, “b”, “c”.
- Parameters:
- namesstr or sequence of str
If a single str, can specify multiple ``Term``s with string containing space or ‘,’ as separator.
- **kwargskeyword arguments
keyword arguments as for
sympy.symbols
- Returns:
- ts
Termor tuple Terminstance or list ofTerminstance objects named from names
- ts
Examples
>>> terms(('a', 'b', 'c')) (a, b, c) >>> terms('a, b, c') (a, b, c) >>> terms('abc') abc