# Gaussian Distribution Power Spectrum

Started by May 31, 2003
 I'm trying to plot the power spec of a set of normally distributed random values. I'm told it should look like a straight line. However, I'm not seeing this. I'm seeing a 'spike' at the beginning, or at the end, depending on the shift. Any thoughts? As you can see, I'm a beginner at Matlab, so places where for loops exist can be replaced with one line. Thanks for the help. function y=Gaussian() fn = 1000; % sampling frequency % randn('seed',5); % this takes all the randomness % out. Verification purposes only run = 64; sample_count = 2^11; % number of discrete samples sample_run = sample_count - run; % we'll get 40 samples over a % our period. for bv = 1:sample_count inphaset(bv) = randn; % initialize data vector end inphase(run) = 0; % initialize the space requireed for dv = 1:sample_run for dx = 1:run inphase(dx) = inphase(dx) + inphaset(dv+dx); end end y = fft(inphase); %Compute FFT of data in inphase % move the DC component to center. ytshift(y); sec = length(inphase)/fn; %Compute the number of seconds of data (acq. rate = 1000) y(1) =[]; %Delete the first value of the resulting array, which is the total relative magnitude mag = abs(y).^2; %Compute square of the magnitude of the FFT (Note that a Fourier transform is a complex function). The magnitude squared gives the power spectrum. power = mag(1:ceil(length(mag)/2)); %Compute the power spectrum from mag as 1/2 the array (use only positive frequencies which are in the first 1/2 of the resulting array) x = (0:length(power)-1)/sec; %Compute the frequencies (x-values) to match the above magnitudes, scaled to the actual number of seconds figure(1); plot(x,power) %Plot the frequency spectrum as Power vs. X y = x;