Comment #41 on issue 1026 by asmeurer: pypy doesn't run sympy
http://code.google.com/p/sympy/issues/detail?id=1026
The problem is
p1 = Piecewise((1,Interval(0,1,False,True)),(0,True))
p2 = piecewise_fold(expand((1-x)*p1))
The issue is that Python gives
In [4]: p2
Out[4]:
⎧ -x + 1 for [0, 1)
⎪
⎨⎧-x for [0, 1) otherwise
⎪⎨
⎩⎩0 otherwise
and PyPy gives:
p2
⎧ -x + 1 for [0, 1)
⎪
⎨⎧1 for [0, 1) otherwise
⎪⎨
⎩⎩0 otherwise
But these are actually the same , since the part that's different is never
true.
But there's actually a more serious issue with Piecewise demonstrated by
this test failure. We have (from the test):
In [10]: p1 = Piecewise((1,Interval(0,1,False,True)),(0,True))
In [11]: p1
Out[11]:
⎧1 for [0, 1)
⎨
⎩0 otherwise
But this makes no sense. [0, 1) is not a conditional. It should be
something like In(x, Interval(0, 1, False, True)).
If you use an actual conditional, you get the same answer in both Python
and PyPy (though again, this is not guaranteed, as the second part is never
true):
p1 = Piecewise((1,Or(x >= 0, x < 1)),(0,True))
p2 = piecewise_fold(expand((1-x)*p1))
p2
⎧ -x + 1 for x < 1 ∨ 0 ≤ x
⎪
⎨⎧1 for x < 1 ∨ 0 ≤ x otherwise
⎪⎨
⎩⎩0 otherwise
In [19]: p1 = Piecewise((1,Or(x >= 0, x < 1)),(0,True))
In [20]: p2 = piecewise_fold(expand((1-x)*p1))
In [21]: p2
Out[21]:
⎧ -x + 1 for x < 1 ∨ 0 ≤ x
⎪
⎨⎧1 for x < 1 ∨ 0 ≤ x otherwise
⎪⎨
⎩⎩0 otherwise
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