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sqrt(x).is_negative returns False instead of None #18597

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merged 6 commits into from Feb 9, 2020
Merged

sqrt(x).is_negative returns False instead of None #18597

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a115f2b
sqrt is negative return False
Smit-create Feb 7, 2020
4302440
Merge branch 'master' into 14815
Smit-create Feb 7, 2020
22c7657
sqrt fix for is_extended_negative
Smit-create Feb 7, 2020
628f7da
suggested changes
Smit-create Feb 9, 2020
297bc62
suggested change
Smit-create Feb 9, 2020
c8d0984
additonal tests
Smit-create Feb 9, 2020
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3 changes: 3 additions & 0 deletions sympy/core/power.py
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Expand Up @@ -530,6 +530,9 @@ def _eval_is_extended_positive(self):
return log(self.base).is_imaginary

def _eval_is_extended_negative(self):
if self.exp is S(1)/2:
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is works here because 1/2 is singletonized, but it's generally better to be explicit about that and use S.Half if you are using is (otherwise use ==).

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We should be able to generalize this.

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Okay I would change that and keep it correct next time. Should I commit this to same branch?

if self.base.is_complex or self.base.is_extended_real:
return False
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if self.base.is_extended_negative:
if self.exp.is_odd and self.base.is_finite:
return True
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13 changes: 13 additions & 0 deletions sympy/core/tests/test_power.py
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Expand Up @@ -510,6 +510,19 @@ def test_issue_18190():
assert sqrt(1 / tan(1 + I)) == 1 / sqrt(tan(1 + I))


def test_issue_14815():
x = Symbol('x', real=True)
assert sqrt(x).is_extended_negative is False
x = Symbol('x', real=False)
assert sqrt(x).is_extended_negative is None
x = Symbol('x', complex=True)
assert sqrt(x).is_extended_negative is False
x = Symbol('x', extended_real=True)
assert sqrt(x).is_extended_negative is False
assert sqrt(zoo, evaluate=False).is_extended_negative is None
assert sqrt(nan, evaluate=False).is_extended_negative is None


def test_issue_18509():
assert unchanged(Mul, oo, 1/pi**oo)
assert (1/pi**oo).is_extended_positive == False