Comment #151 on issue 1694 by nicolas.pourcelot: solve has many issues with
fractions
http://code.google.com/p/sympy/issues/detail?id=1694
So, "all symbols are positive" is a sufficient condition (while not
necessary).
I mean, if 'a', 'x' and 'y' are positive reals, you have both:
a*log(x) == log(x**a)
and
log(x) + log(y)
Just like, for powdenest(), (x**y)**z = x**(y**z), all symbols being
positive is a sufficient condition, but the equality is verified in other
cases (for example, if z is an integer...)
Another approach would be to have a more generic keyword, something
like 'force=True'.
Well, imo, the API should be as much as possible unified, while it's up to
the user to have some mathematic notions if he wants to force powdenest()
or logcombine() behavior... or, at least, to read the help included in the
corresponding docstrings - for example, Chris' powdenest() is much
documented.
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