Comment #1 on issue 3052 by [email protected]: evaluating Abs should
result in a positive number
http://code.google.com/p/sympy/issues/detail?id=3052
I'm not sure if this is fixable. Once you substitute in a number, abs
evaluates it:
In [30]: print e.subs(x,Rational('.1'))
-3.14159265358979e+20*cos(1/10)**2 - 3.14159265358979e+20*sin(1/10)**2 +
3.14159265358979e+20
So by the time you call .n(), the abs is gone. Since the number is really
zero, it's going to give you something really close to zero, but with the
abs gone, it could appear on either side.
Actually, I think the default precision results in a negative number:
In [32]: e.args[0].subs(x,Rational('.1')).n()
Out[32]: -.0e-118
so Abs() evaluates it to its negative.
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