Power Spectral Density from jTransforms DoubleFFT_1D

Question

I\'m using Jtransforms java library to perform analysis on a given dataset.

An example of the data is as follows:

980,988,1160,1080,928,1068,1156,11         


        

Answer 1

To get the magnitude of bin k you need to calculate sqrt(re * re + im * im), wheer re, im are the real and imaginary components in the FFT output for bin k.

For your particular FFT re[k] = a[2*k] and im[k] = a[2*k+1]. Therefore to calculate the power spectrum:

for k in 0 to N/2 - 1
  spectrum[k] = sqrt(sqr(a[2*k]) + sqr(a[2*k+1]))