This file is created to depict the differences between 'spectrum' from TISEAN and 'fft' from GNU Octave. They are essentially the same, but the data output from 'fft' needs to formated to fit onto 'spectrum'. This can be viewed by looking at 'test_spectrum.m'.  

1. Actual differences
Apart from the data presented in a different form the biggest issue that seems to arrise in the step response. It seems like the 'spectrum' behaves differently than the data obtained from 'fft'. It seems as though the data from 'fft' is more likely to be accurate.


2. Different usage

  $ spectrum data.dat -o "data_spec.dat"

  n = length (data);
  half_n = floor (n/2) + 1; 
  spec = fft (data);
  spec = data_spec(1:half_n);
  spec = abs (spec(1:half_n) / n).^2;  
  freqs = [0:half_n-1] / n ;
  data_spec = [freqs,spec];

When the flags '-f' and '-w' become different that the default it becomes a little more complex to make the data align. Taking '-f' and '-w' under consideration was implemented in 'test_spectrum.m'.
