Hey,

I'm very new to both python and sympy but while trying to do some
symbolic calculations, I ran into a lot of trouble with non-
commutative symbols. I read the following issue posts and am having
similar problems:

Issue 1358: http://code.google.com/p/sympy/issues/detail?id=1358
Issue 960: http://code.google.com/p/sympy/issues/detail?id=960&q=commutative
Issue 1261: http://code.google.com/p/sympy/issues/detail?id=1261&q=commutative

I tried applying the patch to sympy.core.mul given in Issue 1358 by
user yaukwankiu. Although it fixed problems like

>import sympy as sp
>a,b,c = sp.symbols('abc', commutative=False)
>(a*b*a*b).subs(a*b,c)
c**2

which is right, it still doesn't fix problems like

>sp.collect(c*a*b-b*a*c,c)
c*(a*b - b*a)

>sp.symbols('d',commutative=True)
>d*a*b.subs(a*b,b*a + c)
d*a*b.

Any help on this issue would be great because I will be doing many of
this-type calculations all summer. Looking forward to your help.



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