Comment #4 on issue 3052 by [email protected]: evaluating Abs should
result in a positive number
http://code.google.com/p/sympy/issues/detail?id=3052
Thanks to the magic of git, I found it in your equals branch.
That routine is about determining if a function is zero (this can be broken
by making a function zero inside the domain where it checks, using
Heaviside for example). This problem is much simpler. We are trying to
determine if a single number is zero (an expression with no free symbols).
I think we must use the precision to determine where to cut off at zero.
If the expression is purely symbolic, we can try extending the precision
until it gives a definite sign, but due to the table maker's dilemma, there
is no way to tell how far to go (and indeed, if the expression is
identically zero, you will never go far enough).
If on the other hand the expression contains floats with precisions, I
think those would have to bound the precision of the final expression. Is
there an easy way to tell the one case from the other?
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