the IFFT returns zeros

2013 1 16
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Hi,
I'm trying to do a deconvolution with the formula from a standard (to check if it returns the same results as the function "deconv"):
ifft( fft(h1) / fft(h2) )
fft(h1) / fft(h2) gives me a NxN matrix as expected. However, only one column is different to zeros(:,1), but it can make sense.
Then, when I try to do the inverse fast Fourier transform, Matlab often returns only zeros !
Here is the part of my code:
if true
AA=fft(a(:,4),siz_ft);
BB=fft(a(:,3),siz_ft);
CC=AA/BB;
DD=ifft(CC,siz_ft);
for k=1:siz_ft
if DD(:,k)~=zeros(siz_ft,1)
DD(1:4,k)
end
end
end
It means that DD returns something only 4 times over 16 different measures.
Does anyone have an idea about my problem ?
Thank you for any help !

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Matt J
Matt J 2013-1-16
编辑：Matt J 2013-1-16

0 个投票

For starters, I think you need to be doing elementwise division.
CC=AA./BB
Beyond that, it's not clear from your description what you're seeing. First you say your seeing all zeros and then you say "DD returns something only 4 times over 16 different measures" which I assume to mean is not all zeros.
I'm also not sure how you're able to loop over DD(:,k) without getting an error message, because in your code DD only has 1 column.

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Ambroise WALLYN
Ambroise WALLYN 2013-1-16
编辑：Ambroise WALLYN 2013-1-16

0 个投票

Hi, thank you for your answer !
So, I already find that it works with elementwise division but I thought it was not correct...
Then, I'm sorry not being clear enough :
the code I wrote is part of a loop from 1 to 16 (where a(:,3) and a(:,4) change) and so DD returns something only 4 times over the 16 measures from the loop
Finaly, I don't have an error message since CC=AA/BB returns a matrice n-by-n
Whatever, thank you for your answer, since the element-wise division AA./BB works !

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Matt J
Matt J 2013-1-16
OK. If my answer helped, you are encouraged to Accept-click it formally (my Answer, not your response).
Ambroise WALLYN
Ambroise WALLYN 2013-1-18
Ok, sorry. I've just done it Thank you again

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