Comment #3 on issue 3052 by [email protected]: evaluating Abs should result in a positive number
http://code.google.com/p/sympy/issues/detail?id=3052
It's not hard to generate numerical zeros. Just take two expressions that are identically equal to each other but are computed differently (in this case, you have sin(x)**2 + cos(x)**2 and 1).
How does the numerical_zero algorithm work? Given the existence of the table maker's dilemma, I would suspect that any algorithm would be technically breakable.
I agree that using evalf() to make decisions about the sign of an expression without consideration of the precision when the expression is near zero is troubling.
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