CODEWITHSUNDEEP
matlab
BillyJean
BillyJean

Reputation: 1577

inverse fft with matlab not working

I am trying to do an inverse FFT in Matlab, but I can't seem to get the inverse working correctly. Here is my code:

    data = [-0.0005
       -0.0004
       -0.0003
       -0.0002
       -0.0001
       -0.0000
        0.0001
        0.0001
        0.0001
        0.0002
        0.0002
        0.0002
        0.0002
        0.0002
        0.0002
        0.0002
        0.0002
        0.0002
        0.0003
        0.0004
        0.0005
        0.0006
        0.0007
        0.0009
        0.0010
        0.0011
        0.0011
        0.0012
        0.0011
        0.0011
        0.0011
        0.0010 ];    


%plot data
figure(1)
plot(data)    

%FFT
N = 100;
X = fft(data, N);
F = [-N/2:N/2-1]/N;
F = F/0.0125;

X = fftshift(X);
figure(2)
plot(F, abs( X ) )

%inverse FFT
y = ifft(X);
figure(3)
plot(F,y)

Figure 1 and 3 should be identical, but are not in any way. I made sure not to take ifft of the absolute value of fft, so it's not clear to me what is wrong.

Upvotes: 0

Views: 223

Answers (1)

Suever
Suever

Reputation: 65430

Since you shifted the spectrum using fftshift, you have to "unshift" the spectrum prior to taking the inverse Fourier transform

y = ifft(fftshift(X));

Upvotes: 1

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