Hi to all Sympy-people,
while doing some calculations I stumbled over some strange behavior in
the Sum function. I don't know, if I just misuse it or if something is
broken.
I try to calculate this:
m = Symbol('m')
I = Symbol('I')
s = Sum(exp(m), (m, -I, I))
# m should be -2 .. 2
s = s.subs(I,2).doit()
print(s)
# prints: (exp(-I) - exp(1 + I))/(1 - E)
s.subs(I,2).evalf()
# 11.61... the correct result
# now just slightly different:
s = Sum(m*exp(m), (m, -I, I))
# m should be -2 .. 2
s = s.subs(I,2).doit()
print(s)
# Sum(m*exp(m), (m, -I, I)), so it did not expand
# infinite loop here:
s.subs(I, 2).evalf()
So, how should this be done correctly or is the Sum function only
working in special cases?
Thanks for any help!
Alexander
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