MATLAB: How to get a period of cosinus function

period

Hi,
I have to find the period of the cosinus function using only the vector time and the vector data of the function.
Cosinus function
Vector data
time data

Best Answer

Because this is homework, I won't provide a copy-paste ready solution.
If you follow the example from the documentation for fft, you get the code below.
%recreate data
delta_t=0.1;Tlim=5;f=[1;2];
t=0:delta_t:Tlim;
x=sum(cos(2*pi*t.*f));
%figure(1),clf(1)
%plot(t,x)
Fs=1/mean(diff(t));%sampling frequency
L=numel(x);
Y = fft(x);
P2 = abs(Y/L);
P1 = P2(1:floor(L/2)+1);
f = Fs*(0:(L/2))/L;
figure(1),clf(1)
plot(f,P1,'-*')
title('Fourrier transform'),xlabel('frequency'),ylabel('magnitude')
Now you can clearly see there are two frequencies that have a high magnitude.
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