% function to do fast fourier transform on the signal
% Usage [k,s] = fourier(x)
% 
% where k is index from 0 to N-l
%       x is the input signal
%       s is the power spectrum
%	N is the length of the series
%
% The spectrum is symmetrical about the middle, corresponding to negative
% frequency. Use only the first half of the spectrum for the pset.
 

function [k,s] = fourier(x)

N = length(x);
k = 0:N - 1;
s = abs(1/sqrt(N)*fft(x)).^2;

%To plot spectrum, type
%>> plot(k,s);