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matlabfftconvolutionfrequency-domain
David Webb
David Webb

Reputation: 128

Why does convolution via multiplication in the frequency domain produce unexpected results MATLAB?

I'm trying to convolve a rectangular pulse with itself by taking the Fourier transform, squaring it, and then taking the inverse Fourier transform. I realize there is a conv() function but I would prefer to do it in the frequency domain for future, more complex problems. My problem is that when I do this, it does not produce a triangular function as expected. The code I'm using is below:

clc

clear all

x=-5:.01:5;

y=rectangularPulse(x);

Y=fft(y);

H=Y.^2;

h=ifft(H);

plot(x,h)

Upvotes: 0

Views: 1191

Answers (1)

AnonSubmitter85
AnonSubmitter85

Reputation: 933

You need to zeropad in order to ensure that the convolution is linear. Currently you are performing a circular convolution. Try something like this:

y = ones(100,1);    
N = length(y);
Nfft = 2*length(y) - 1;

Y=fft(y,Nfft);
H=Y.^2;
h=ifft(H);
plot(h);

Upvotes: 2

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