How to calculate period of signal with matlab

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

[Azzi Abdelmalek]

This is not clear, do you have samples or what?

Answer 1

[Mohammad Abouali]

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.

[Ibrahim Ashraf]

What is the value that you consider high in the first example. is it above 1?

[Anuj Patel]

What is the other FFT approach , sir?

[Lucky Moffat]

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.

Answer 2

[Firstname Lastname]

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']);

[OSAMA MOHAMED ALI]

can I use it for discrete signals?