When I have
Sum[(-1)^n x^(n^2) y^n, {n, 0, ∞}]
and I try evaluating
Series[Sum[(-1)^n x^(n^2) y^{n}, {n, 0, ∞}], {x, 0, 3}, {y, 0, 2}]
it does not return the terms in the series that I want.
I am not interested in changing my Sum
expression to be finite as in, say, {n, 0, 3}
instead of {n, 0, ∞}
, because I will be making many such functions defined as infinite series and will want to constantly manipulate them using algebraic operations, so I will be generating multiple series. This also means I need to keep the operation Series
, since I will be feeding, e.g., products of such sums with other functions.