Status: Accepted
Owner: ----
Labels: Type-Defect Priority-Medium
New issue 3167 by [email protected]: e.is_integer wrong
http://code.google.com/p/sympy/issues/detail?id=3167
>>> e = -3 - sqrt(5) + (-sqrt(10)/2 - sqrt(2)/2)**2
>>> e.is_integer
False
>>> ask(Q.integer(e))
False
In both cases, it should return None (at worst) or True (at best). It
falters in the old system because it is assumed that if all the terms are
not integers then an Add cannot be an integer. While the positive can be
affirmed (if all terms are integers the result is an integer), the reverse
cannot be (if any term is not an integer then the result cannot be an
integer). It would be true that if one term were not an integer then the
result is not an integer, but cancellation in two terms is what causes the
problem.
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