Power spectrum and periodicity

I have a data of length 336 (336 days) having a frequency of an event.

1. 3
2. 1
3. 0
4. 0
5. 2
6. so on to 336

how can I plot power spectrum and periodicity of this data?

thank you

Answer 1

[Star Strider]

There are a number of functions in the Spectral Estimation section of the Signal Processing Toolbox documentation that will work.

For a simpler approach, since power is the square of amplitude, do a Fourier transform (fft) on the element-wise square of the original signal:

M = [(1:365).' rand(365,1)];                        % Original Data
L = size(M,1);
Ts = M(2,1) - M(1,1);                               % Sampling Interval
Fs = 1/Ts;                                          % Sampling Frequency
Fn = Fs/2;                                          % Nyquist Frequency
s = M(:,2);                                         % Signal Vector

NFFT = 2^nextpow2(L);                               % For Efficiency
FTs2 = fft(s.^2,NFFT)/L;                            % Fourier Transform
Fv = linspace(0, 1, NFFT/2+1)*Fn;                   % Frequency Vector
Iv = 1:numel(Fv);                                   % Inmdex Vector

figure
plot(Fv, abs(FTs2(Iv)))
grid
xlabel('Frequency (Cycles/Day)')
ylabel('Amplitude')

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