I'm using Jtransforms java library to perform analysis on a give dataset.
An example of the data is as follows: 980,988,1160,1080,928,1068,1156,1152,1176,1264
I'm using the DoubleFFT_1D funtion in jTransforms. The data output is as follows: 10952, -152, 80.052, 379.936, -307.691, 12.734, -224.052, 427.607, -48.308, 81.472
I'm having trouble interpreting the output. I understand that the first element in the output array is the total of the 10 inputs (10952). It's the other elements of the output array that i don't understand. Ultimately, I want to plot the Power Spectral Density of the input data on a graph and find amounts between 0 and .5 Hz.
The documentation for the jTransform functions states:
(where a is the data set) .....................
realForward
public void realForward(double[] a)Computes 1D forward DFT of real data leaving the result in a . The physical layout of the output data is as follows:
if n is even then
a[2*k] = Re[k], 0 <= k < n / 2
a[2*k+1] = Im[k], 0 < k < n / 2
a[1] = Re[n/2]
if n is odd then
a[2*k] = Re[k], 0 <= k < (n+1)/2
a[2*k+1] = Im[k], 0 < k< (n-1)/2
a[1] = Im[(n-1)/2]
This method computes only half of the elements of the real transform. The other half satisfies the symmetry condition. If you want the full real forward transform, use realForwardFull. To get back the original data, use realInverse on the output of this method.
Parameters: a - data to transform ..................................
So what are the output numbers? What do the values mean? Any help is appreciated.