Updates:
Labels: NeedsReview smichr
Comment #7 on issue 2043 by asmeurer: log should not expand(1/x)
(was "expand log can be more complete" and "logcombine can be less strict")
http://code.google.com/p/sympy/issues/detail?id=2043
Making all symbols positive is not sufficient to do all operations. If x
and y are positive, x - y could still be negative, meaning you still can't
do anything with log((x - y)*(x + y)) if you want to be rigorous.
Instead of forcing assumptions on the arguments of the log itself, I think
it should instead be possible to assume that log itself is a real-valued
function. It could be with the new assumptions with something like
Assume(log, Q.real), or maybe a kwarg to log (log(x, real=True)), though
the easiest way is to just make all important functions that do log
manipulation have symbolic kwargs.
On the other hand, I really do thing as I mentioned before somewhere that
it could be useful to have some kind of "meta-assumption" in the new
assumptions, along the lines of Assume(expr, Q.nice_things) (maybe
Q.symbolic) that does what your posify is purporting to do.
--
You received this message because you are subscribed to the Google Groups
"sympy-issues" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/sympy-issues?hl=en.
