CODEWITHSUNDEEP
sympy
Martin C. Martin
Martin C. Martin

Reputation: 3672

Collecting all terms involving factor in sympy

I have an expression where three terms involve r**2, I'd like to collect those together and factor out the r**2:

>>> foo = a**2*r**2 + 2*a*b*x*r + 2*a*b*r**2 + b**2 + 2*b**2*r + b**2*r**2
>>> foo
 2  2          2                2  2      2      2
a ⋅r  + 2⋅a⋅b⋅r  + 2⋅a⋅b⋅r⋅x + b ⋅r  + 2⋅b ⋅r + b

simplify doesn't alter the expression at all.

In my actual use case, foo is actually a subexpression: I'm dividing by the coefficient of r**2, so that will cancel off for that term, and everything is under a square root.

So the general question is: if I want to effect a transformation of a subexpression, e.g. factoring certain terms, how do I do that on a sub expression, as opposed to the whole expression?

Upvotes: 0

Views: 170

Answers (1)

Oscar Benjamin
Oscar Benjamin

Reputation: 14480

You can use collect:

In [84]: collect(foo, r**2)
Out[84]:
               2      2    2 ⎛ 2            2⎞
2⋅a⋅b⋅r⋅x + 2⋅b ⋅r + b  + r ⋅⎝a  + 2⋅a⋅b + b ⎠

Upvotes: 1

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