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Comment #2 on issue 1495 by smichr: minus problem
http://code.google.com/p/sympy/issues/detail?id=1495
I got an infinite recursion from could_extract_minus_sign() when checking
the
expression: x*(-2*a*x - 2*x**3).
I also note that the routine has the test for multiplicative terms:
if den != 0
but I think that should be "den != 1". And then I'm not sure of the logic
that should
follow that so I'm hesitant to do more. Should the test for a
multiplicative term
just be something like the following? Note that no check for den (or num)
being "1"
is done since these terms are no problem to check.
elif self.is_Mul:
num, den = self.as_numer_denom()
return len([1 for tmp in num.args if tmp.could_extract_minus_sign()]+ \
[1 for tmp in den.args if tmp.could_extract_minus_sign()])%2
Although this code works for answering the question of whether a minus
could be
factored out, it doesn't resolve the issue of getting something into
canonical form, e.g.
>>> -x*(-2*a*x - 2*x**3)
-x*(-2*a*x - 2*x**3)
We would like to see x*(2*a*x + 2*x**3) instead, right?
I can copy this to a new issue if deemed necessary.
I'm putting this as a high priority because a simple question should not
give an
infinite recursion ;-)
/c
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