Comment #37 on issue 2607 by [email protected]: as_numer_denom() is too slow
http://code.google.com/p/sympy/issues/detail?id=2607
Re #35
right, it doesn't work. Although an entire Mul is cached, when you multiply
that by another Mul, all the args are reprocessed. I checked this with Add
but the same should apply to Mul:
I put print seq at the start of the flatten routine to see when it is
called.
Using + builds up the result one pair at a time
>>> x+y+z
[x, y]
[x + y, z]
x + y + z
whereas feeding it to Add lets them all be processed at once
>>> Add(x,y,z)
[x, y, z]
x + y + z
The result is cached so repeating the Add won't reflatten the args
>>> Add(x,y,z)
x + y + z
>>> x+y+z
x + y + z
But if you add something, everything has to be reflattened
>>> s=_
>>> s+w
[x + y + z, w]
w + x + y + z
>>> Add(s,v)
[x + y + z, v]
v + x + y + z
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