billy :
I have been trying to find the coefficients of some lengthy expressions, and even though they are non zero, the result I take is equal to 0.
I think the problem is that I don't get the result to be (s1+s2)/s4 on this mwe:
Sym1,Sym2,Sym3,Sym4 = sy.symbols('s1, s2, s3, s4')
xx = sy.Symbol('x')
TestExp = Sym1*xx + Sym2*xx + Sym3
print(TestExp.coeff(xx))
TestExp2 = (Sym1*xx + Sym2*xx + Sym3)/Sym4
print(TestExp2.coeff(xx))
smichr :
coeff is pretty literal so if there is no term with xx as a factor then it will return 0. As your expression is, it appears as a fraction, a single term, and there is no factor of xx in that term. (But there is in the numerator.) Try expanding your expression first:
>>> print(TestExp2.expand().coeff(xx))
s1/s4 + s2/s4
And touch it with factor_terms or collect to simplify:
>>> factor_terms(_)
(s1 + s2)/s4
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