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%% Periodogram of Relative Sunspot Numbers % Obtain the periodogram of the Wolf (relative sunspot) number data sampled % yearly between 1700 and 1987. % Copyright 2015 The MathWorks, Inc. %% % 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') 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.