I have the following expression multiplying two expressions:
from sympy import *
c1, c2, x = symbols("c1, c2, x")
expr = c2*x*(c1*x + c2*x)
I would like to be able to open the parenthesis, so that this expression would be
c1*c2*x**2 + c2**2*x**2
I need this because I want to analyze each monom separately How can this be done? I tried converting it to Poly and back, but for some reason it causes errors non-deterministically.
It sounds like you just want to use expand:
In [1]: from sympy import *
...: c1, c2, x = symbols("c1, c2, x")
...: expr = c2*x*(c1*x + c2*x)
In [2]: expr
Out[2]: c₂⋅x⋅(c₁⋅x + c₂⋅x)
In [3]: expr.expand()
Out[3]:
2 2 2
c₁⋅c₂⋅x + c₂ ⋅x
Poly should also work and should be deterministic (I suspect you have made some other error if you think it is non-deterministic):
In [4]: Poly(expr)
Out[4]: Poly(x**2*c1*c2 + x**2*c2**2, x, c1, c2, domain='ZZ')
In [5]: Poly(expr).as_expr()
Out[5]:
2 2 2
c₁⋅c₂⋅x + c₂ ⋅x
You can also get a mapping of monomials and coefficients without converting to Poly using as_coefficients_dict:
In [6]: dict(expr.expand().as_coefficients_dict())
Out[6]:
⎧ 2 2 2 ⎫
⎨c₂ ⋅x : 1, c₁⋅c₂⋅x : 1⎬
⎩ ⎭