Dear MKL forum,

I solve such a problem. Can you help me please?

Lets have a function Y=∑ _{k=−∞}^{∞} iY_{n}e^{ikπy} and then I have a function which is defined as X=∑_{k=−∞}^{∞} ik^{2}Y_{n}e^{ikπy}.

I know the *Y*. The *i* is imaginary unit.

How can I compute the *X*? I think I do the FFT on *Y* and obtain thus the Y_{n}, right? And then I think I will do the backward FFT of function defined as f=ik^{2}Y_{n}. But what have I do with the summation index *k* here in the function *f*?

It is right that FFT(ik^{2}Y_{n})=X?

I'm not sure absolutely what to do with *k* when the FFT sum is summated per *k*. Or can I change something in MKL FFT directly?