Comment #9 on issue 3710 by [email protected]: shallow expansion
feature/bug
http://code.google.com/p/sympy/issues/detail?id=3710
This is the intended expansion in the codebase when expand_mul is used.
Since deep is automatically True, this also recurses through the entire
tree making changes that won't be processed at the level that a
simplification routine is likely working at. e.g. if I want to extract
the gcd from an expression, I would flatten it, leaving contents of cos,
for example, alone since the interior won't leak out, and then run over
the factors of each term looking for gcds.
I've noticed that whenever expand_mul is used, usually expand_multinominal
is also desired. So perhaps we should just create a special helper to
expand that just does "smart" expand_mul + expand_multinomial. You want to
expand the top level expression as a polynomial, right?
Imagine using expand_mul(deep=True) in a bottom up simplification: every
time it gets used it drills down through the already expanded tree when
all that is actually needed is to flatten the current level wrt Add and
Mul.
But why wouldn't deep=False work in that case? The way deep=False works
now seems like a perfect match for bottom up simplification.
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