Status: Accepted
Owner: [email protected]
Labels: Type-Defect Priority-High Assumptions Python3 WrongResult
New issue 2574 by [email protected]: Wrong assumptions for LambertW(-1)
http://code.google.com/p/sympy/issues/detail?id=2574
With master:
In [1]: LambertW(-1).is_comparable
Out[1]: True
In [2]: LambertW(-1).is_positive
Out[2]: True
In [3]: LambertW(-1)._assumptions
Out[3]: {commutative: True, comparable: True, complex: True, imaginary:
False, negative: False, nonnegative: True, nonpositive: False, nonzero:
True, positive: True, real: True, zero: False}
In [4]: LambertW(-1).evalf()
Out[4]: -0.318131505204764 + 1.33723570143069⋅ⅈ
The root issue is the first line: LambertW(-1).is_comparable == True. This
is particularly problematic in the Python3 port, because it causes
LambertW(-1).is_positive to raise.
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