I want to find all frequencies of a signal (an array of double values) where each samples are taken at the same interval (5 minutes).

I tought I could use:

MathNet.Numerics.IntegralTransforms.Fourier.Forward(new double[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 });

But there is 2 bugs. The function takes Complex[], not double[]. There is no result, only “void” is returned.

So any idea what I should call and where I could find results: frequencies, angle and amplitude?

By the way, my signal has 2 main frequencies: By year and by day. Does an FFT can find both frequencies (year and day) either if a day is 1/365 of a year frequency?

What is the minimum signal lenght to find year frequency (2 years as NYQIST said)?