Status: Accepted
Owner: asmeurer
Labels: Type-Defect Priority-Medium Simplify NeedsReview

New issue 1565 by asmeurer: powsimp() does not combine exponents in some  
cases.
http://code.google.com/p/sympy/issues/detail?id=1565

powsimp does not combine exponents correctly in the following case, for  
example: exp(x)/(1 +
exp(x)*exp(y)).  This is because the exponentials to be combined are inside  
of a larger exponential ( (1
+ exp(x)*exp(y))**(-1) ), and powsimp doesn't handle that correctly.

I have fixed it.  Please pull from  
http://github.com/asmeurer/sympy/tree/powsimp-fix.

Note that you need to use deep=True to combine the above example.

Unfortunately, powsimp() no longer calls separate(), so x**n * (x*n)**(-n)  
* n will be simplified into
n*n**-n rather than n**(1 - n).  This is because separate() was messing up  
simplification of
expressions like (z**x*z**y)**x.  See the log for more info.

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