subs in a sum

[Thomas Ligon]

Here is a code snippet (for test purposes):

from sympy import symbols, I, oo, Sum, exp

a, s, t, j = symbols('a s t j')

ex = Sum(a*exp((2*s + 1)*I*t), (s, -oo, oo))

print(ex)

ex = ex.subs(s, j)

print(ex)

The subs statement has no effect. Is there another way to do this?

[Aaron Meurer]

subs() doesn't replace s because it is a bound variable. You can use
replace or xreplace to do it.

>>> Sum(a*exp((2*s + 1)*I*t), (s, -oo, oo)).xreplace({s: j})
Sum(a*exp(I*t*(2*j + 1)), (j, -oo, oo))

Aaron Meurer

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[Thomas Ligon]

Thanks! I tried both replace and xreplace (to learn more) and they both worked for me, so I chose replace, since it looks simpler.