Comment #10 on issue 1827 by asmeurer: log eval gives more standard form
http://code.google.com/p/sympy/issues/detail?id=1827
logcombine can do that, but you have to have the proper assumptions on x,
or else use the assume_pos_real flag:
In [14]: logcombine(x*log(10)-x*(log(2)+log(5)), assume_pos_real=True)
Out[14]: 0
In [15]: x = Symbol('x', real=True)
In [16]: logcombine(x*log(10)-x*(log(2)+log(5)))
Out[16]: 0
So you probably have code duplication. logcombine is supposed to be the
opposite of expand(log=True) anyway.
I don't know how you would stop Python from evaluating 2**reallybignumber
before log gets to it. The only option is to
pass it to Pow with eval=False, or maybe sympify could be smart enough
about it. Actually, the evaluate=False gives some
other bug, which seems to show up every time you try to do seomthing with
an evaluate=False expression:
In [17]: log(Pow(2,9182340981273490812734, evaluate=False))
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
[…]
AttributeError: is_commutative
And I'm actually starting to think that maybe it could be in eval, if there
is a limit on the factors :) But just the log eval. If
the user wants more complex simplification, he can use expand(log=True) or
logcombine.
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