Comment #3 on issue 3312 by laurence.gonsalves: "RuntimeError: maximum
recursion depth exceeded" in sympy.cse
http://code.google.com/p/sympy/issues/detail?id=3312
Here's a workaround:
def AppliedUndef__lt__(self, other):
if type(self) != type(other):
return type(self) < type(other)
return self.args < other.args
sympy.function.AppliedUndef.is_negative = False
sympy.function.AppliedUndef.__lt__ = AppliedUndef__lt__
Actually, setting is_negative turns out to not be strictly necessary once
__lt__ is defined, but without setting it this way cse will do things like:
tmp0 = f(1)
tmp1 = -tmp0
and then never use tmp0 again. For example:
...
>>> sympy.function.AppliedUndef.__lt__ = AppliedUndef__lt__
>>> a = sympy.Function('a')
>>> b = sympy.Function('b')
>>> ma = sympy.Matrix([[a(0),a(1)], [a(2),a(3)]])
>>> mb = sympy.Matrix([[b(0),b(1)], [b(2),b(3)]])
>>> # at this point __lt_ has been patched, but not is_negative
>>> sympy.cse(ma*mb)
([(x0, a(0)), (x1, a(1)), (x2, b(2)), (x3, b(0)), (x4, a(2)), (x5,
b(1)), (x6, a(3)), (x7, b(3)), (x8, -x7), (x9, -x2), (x10, -x0), (x11,
-x4)], [-x1*x9 - x10*x3, -x1*x8 - x10*x5, -x11*x3 - x6*x9, -x11*x5 - x6*x8])
>>> sympy.function.AppliedUndef.is_negative = False
>>> sympy.cse(ma*mb)
([(x0, a(0)), (x1, a(1)), (x2, b(0)), (x3, b(2)), (x4, a(2)), (x5,
b(1)), (x6, a(3)), (x7, b(3))], [x0*x2 + x1*x3, x0*x5 + x1*x7, x2*x4 +
x3*x6, x4*x5 + x6*x7])
Note how the second call to cse eliminates the useless temporaries, and the
end result also has less (negating) operations.
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