I have two lines in the code:
print(expr.subs(t,2*l))
print(simplify(expr.subs(t,2*l)))
Which yield:
2*Sum(2**(-2*j + 2*l + 1)*2**(2*j + 2*l - 3)*(l + 1)**2*factorial(-j + 2*l + 1)*factorial(j + 2*l - 1)/((-j + l + 1)*(j + l - 1)*factorial(j)*factorial(2 - j)*factorial(-2*j + 2*l + 1)*factorial(2*j + 2*l - 3)), (j, 0, 0))
0
The first command works correctly and the expression is what it should be, but somehow the output of the second command is 0.
When I calculate this doubled sum manually, it is not 0. There is only one term in the sum (as j goes from 0 to 0).
Can somebody explain why the last command returns 0?
5