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How to calculate period of signal with matlab

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Ioannis
Ioannis 2014-11-30
编辑： OSAMA MOHAMED ALI 2024-4-23
Hi everybody, I have the signal x2(t)=|cos(10*pi*t)|.How can i calculate its period with matlab?I am new matlab so each help will be usefull

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Mohammad Abouali
Mohammad Abouali 2014-12-1
编辑：Mohammad Abouali 2014-12-1
use autocorrelation. If your data is periodic you should get high correlation once the lag time matches the period. here is an example:
x=0:0.1:20*2*pi;
y=sin(x); % so we know the period is 2*pi roughly 6.28
ac=xcorr(y,y);
[~,locs]=findpeaks(ac);
mean(diff(locs)*0.1)
ans =
6.2842
In a more complex data set including some noise you need to work around the find peaks a little bit. That might be too noisy.
In the example you gave here is what you will get
x=0:0.01:20*2*pi;
y=abs(cos(10*pi*x));
ac=xcorr(y,y);
[~,locs]=findpeaks(ac);
mean(diff(locs)*0.01)
ans =
0.1000
Another approach is using FFT, particularly if you have a more complex signal.
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Lucky Moffat
Lucky Moffat 2023-2-22
Take the FFT of the signal, then compute the power spectrum. Then, determine the frequency index k of maximum power. After this, determine the frequency at index k of maximum power. Once you've found the frequency it's easy to find the period since T = 1/f, e.g.,
t = 0:0.004:4;
sig = cos(2*pi*20*t);
a = fft(sig, 1024);
A = abs(a).^2;
[~, index_max_power] = max(A);
index_freq = index_max_power / ((t(2)-t(1))*length(A));
period = 1/index_freq
So, in that example the period T should be closer to 0.05.

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Firstname Lastname
Firstname Lastname 2017-8-21
编辑：KSSV 2022-7-9
t=0:.01:10;
y=10*sin(10*pi*t);
[idx,idx]=findpeaks(y);
T=t(idx(2))-t(idx(1));
disp(['Time Period =' num2str(T),'seconds']);

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