MATLAB: Please help correct fft command used to compute equation

fft commandhomeworkno attempt

given a discrete-time sinusoid x[n]=10cos(200*pi*t+1.2) where n is between 0 and 100 (including 0 and 100)
With the use of the fft command, i attempted to develop the MATLAB function to compute the follwing equation. Also use the command max in the peak search to determine the peak freqency.
 t = 0:0.001:0.1-0.001;
 x = 10*cos(200*pi*t+1.2); 
 function X = dtft(x, 200*pi) 
 [L1, L] = size(x);
 z = exp(-j*w); X = 0;
 for n = L-1:-1:0,
       X = x(n+1) + z .* X;
 end 
 Y=(X^2)/N
 p = max(X)
no outputs return at all. please help correct. thank u!

Best Answer

"With the use of the fft command..."
where have you used the fft() command?
 Fs = 1000;
 t = 0:0.001:0.1-0.001;
 x = 10*cos(2*pi*100*t+1.2);
 xdft = fft(x);
 xdft = xdft(1:length(x)/2+1);
 freq = 0:Fs/length(x):Fs/2;
 [maxval,idx] = max(abs(xdft));
 freq(idx)
As you see freq(idx) produces the frequency corresponding to the maximum absolute value in the DFT of x.
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