%% Periodogram of Relative Sunspot Numbers
% Obtain the periodogram of the Wolf (relative sunspot) number data sampled yearly between 1700 and 1987.
% Load the relative sunspot number data. Obtain the periodogram using the default rectangular window and number of DFT points (512 in this example). The sample rate for these data is 1 sample/year. Plot the periodogram.

load sunspot.dat
relNums=sunspot(:,2);

[pxx,f] = periodogram(relNums,[],[],1);

plot(f,10*log10(pxx))
xlabel('Cycles/Year')
ylabel('dB / (Cycles/Year)')
title('Periodogram of Relative Sunspot Number Data')

% You see in the preceding figure that there is a peak in the periodogram at approximately 0.1 cycles/year, which indicates a period of approximately 10 years.
% Copyright 2015 The MathWorks, Inc.