Comment #11 on issue 2128 by jagermeistermeister: cannot integrate
piecewise function numerically
http://code.google.com/p/sympy/issues/detail?id=2128
I found out why the error triggers.
In Piecewise._eval_interval there is this code:
if cond.args[0] == sym:
curr[0] = S.NegativeInfinity
elif cond.args[1] == sym:
curr[1] = S.Infinity
else:
raise NotImplementedError, \
"Currently only supporting evaluation with only " \
"sym on one side of the relation."
When I try to integrate(f.subs(x,x-y),(y,-oo,oo)), cond.args[0] becomes
equal to x - y, which is never equal to sym (because sym = y in this case).
I think this could be solved by checking if cond.args[0] contains sym
instead of checking if it is equal to sym. However, I tried searching for
how to accomplish that, without any luck so far :) Could anyone give me a
step in the right direction? I'm still very new to sympy.
My thoughts so far:
1. check if cond.args[0] is an expression
2. if it is an expression, check if cond.args[0] contains sym
3. if it is not an expression, check if cond.args[0] is equal to sym
(the same goes for cond.args[1])
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