I would like to know how to sum up to following series (from the Gradshteyn-Ryzhik tables):
∞∑n=−∞einα(n−β)2+γ2=πγeiβ(α−2π)sinh(γα)+eiβαsinh[γ(2π−α)]cosh(2πγ)−cos(2πβ)
with 0≤α≤2π. In the special case of α=0, we have ∞∑n=−∞1(n−β)2+γ2=πγsinh[2πγ]cosh(2πγ)−cos(2πβ) and I now that I can use the function cot(πz)(z−β)2+γ2 to sum up this series via the residue theorem.
In more detail, the singularities are β±iγ and zn=n, n∈N.
If I sum the corresponding residues, I get what the above result (for α=0).
I am not sure, however:
1) How to choose the contour in order to have a correct argumentation?
2) What to do with the general case α≠0?
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