SymPy - Simplification

simplify

This function is defined in sympy.simplify module. simplify() tries to apply intelligent heuristics to make the input expression “simpler”. Following code shows simplifies expression $sin^2(x)+cos^2(x)$.

>>> from sympy import * 
>>> x=Symbol('x')
>>> expr=sin(x)**2 + cos(x)**2 
>>> simplify(expr)

The above code snippet gives the following output −

expand

The expand() is one of the most common simplification functions in SymPy, used in expanding polynomial expressions. For example −

>>> a,b=symbols('a b') 
>>> expand((a+b)**2)

The above code snippet gives an output equivalent to the below expression −

$a^2 + 2ab + b^2$

>>> expand((a+b)*(a-b))

The above code snippet gives an output equivalent to the below expression −

$a^2 - b^2$

The expand() function makes expressions bigger, not smaller. Usually this is the case, but often an expression will become smaller upon calling expand() on it.

>>> expand((x + 1)*(x - 2) - (x - 1)*x)

The above code snippet gives the following output −

-2

factor

This function takes a polynomial and factors it into irreducible factors over the rational numbers.

>>> x,y,z=symbols('x y z') 
>>> expr=(x**2*z + 4*x*y*z + 4*y**2*z) 
>>> factor(expr)

The above code snippet gives an output equivalent to the below expression −

$z(x + 2y)^2$

>>> factor(x**2+2*x+1)

The above code snippet gives an output equivalent to the below expression −

$(x + 1)^2$

The factor() function is the opposite of expand(). Each of the factors returned by factor() is guaranteed to be irreducible. The factor_list() function returns a more structured output.

>>> expr=(x**2*z + 4*x*y*z + 4*y**2*z) 
>>> factor_list(expr)

The above code snippet gives an output equivalent to the below expression −

(1, [(z, 1), (x + 2*y, 2)])

collect

This function collects additve terms of an expression with respect to a list of expression up to powers with rational exponents.

>>> expr=x*y + x - 3 + 2*x**2 - z*x**2 + x**3 
>>> expr

The above code snippet gives an output equivalent to the below expression −

$x^3 + x^2z + 2x^2 + xy + x - 3$

The collect() function on this expression results as follows −

>>> collect(expr,x)

The above code snippet gives an output equivalent to the below expression −

$x^3 + x^2(2 - z) + x(y + 1) - 3$

>>> expr=y**2*x + 4*x*y*z + 4*y**2*z+y**3+2*x*y 
>>> collect(expr,y)

The above code snippet gives an output equivalent to the below expression −

$Y^3+Y^2(x+4z)+y(4xz+2x)$

cancel

The cancel() function will take any rational function and put it into the standard canonical form, p/q, where p and q are expanded polynomials with no common factors. The leading coefficients of p and q do not have denominators i.e., they are integers.

>>> expr1=x**2+2*x+1 
>>> expr2=x+1 
>>> cancel(expr1/expr2)

The above code snippet gives an output equivalent to the below expression −

$x+1$

>>> expr = 1/x + (3*x/2 - 2)/(x - 4) 
>>> expr

The above code snippet gives an output equivalent to the below expression −

$\frac{\frac{3x}{2} - 2}{x - 4} + \frac{1}{x}$

>>> cancel(expr)

The above code snippet gives an output equivalent to the below expression −

$\frac{3x^2 - 2x - 8}{2x^2 - 8}$

>>> expr=1/sin(x)**2 
>>> expr1=sin(x) 
>>> cancel(expr1*expr)

The above code snippet gives an output equivalent to the below expression −

$\frac{1}{\sin(x)}$

trigsimp

This function is used to simplify trigonometric identities. It may be noted that naming conventions for inverse trigonometric functions is to append an a to the front of the function’s name. For example, the inverse cosine, or arc cosine, is called acos().

>>> from sympy import trigsimp, sin, cos 
>>> from sympy.abc import x, y
>>> expr = 2*sin(x)**2 + 2*cos(x)**2 
>>> trigsimp(expr)

The trigsimp function uses heuristics to apply the best suitable trigonometric identity.

powersimp

This function reduces given expression by combining powers with similar bases and exponents.

>>> expr=x**y*x**z*y**z 
>>> expr

The above code snippet gives an output equivalent to the below expression −

$x^y x^z y^z$

>>> powsimp(expr)

The above code snippet gives an output equivalent to the below expression −

$x^{y+z} y^z$

You can make powsimp() only combine bases or only combine exponents by changing combine=’base’ or combine=’exp’. By default, combine=’all’, which does both.If force is True then bases will be combined without checking for assumptions.

>>> powsimp(expr, combine='base', force=True)

The above code snippet gives an output equivalent to the below expression −

$x^y(xy)^z$

combsimp

Combinatorial expressions involving factorial an binomials can be simplified by using combsimp() function. SymPy provides a factorial() function

>>> expr=factorial(x)/factorial(x - 3) 
>>> expr

The above code snippet gives an output equivalent to the below expression −

$\frac{x!}{(x - 3)!}$

To simplify above combinatorial expression we use combsimp() function as follows −

>>> combsimp(expr)

The above code snippet gives an output equivalent to the below expression −

$x(x-2)(x-1)$

The binomial(x, y) is the number of ways to choose y items from a set of x distinct items. It is also often written as xCy.

>>> binomial(x,y)

The above code snippet gives an output equivalent to the below expression −

$(\frac{x}{y})$

>>> combsimp(binomial(x+1, y+1)/binomial(x, y))

The above code snippet gives an output equivalent to the below expression −

$\frac{x + 1}{y + 1}$

logcombine

This function takes logarithms and combines them using the following rules −

log(x) + log(y) == log(x*y) if both are positive
a*log(x) == log(x**a) if x is positive and a is real

>>> logcombine(a*log(x) + log(y) - log(z))

The above code snippet gives an output equivalent to the below expression −

$a\log(x) + \log(y) - \log(z)$

If force parameter of this function is set to True then the assumptions above will be assumed to hold if there is no assumption already in place on a quantity.

>>> logcombine(a*log(x) + log(y) - log(z), force=True)

The above code snippet gives an output equivalent to the below expression −

$\log\frac{x^a y}{z}$

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