ifft on gpu returns wrong values

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Mojtaba Zarei
Mojtaba Zarei 2021-3-30
评论： Mojtaba Zarei 2021-3-30
I wanted to calculate a 2D FFT on a 3D array and then get the 2D IFFT back. I wanted to use the gpuArray to accelerate the implementation, and I am not sure why I am getting the wrong answer when I have the 3D array on the gpu. For example:
A = fft2(gpuArray(rand(10,10,5)));
A1 = ifft2(A);
A2 = ifft(ifft(A,[],2),[],1);
all(A1==A2,'all')
gpuArray logical
0
A1 = ifft2(gather(A));
A2 = ifft(ifft(gather(A),[],2),[],1);
all(A1==A2,'all')
logical
1
The reason that I used ifft(ifft(A,[],2),[],1) is that I am going to extend the code for a 4D array, and I could not use FFTn to perform a 3D FFT on the first three dimensions! But, when I wanted to get a 3D FFT and then a 3D IFFT using 1d FFT/IFFT, I noticed different GPU and CPU results. Would you please explain what I am doing wrong here?

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采纳的回答

Matt J
Matt J 2021-3-30
编辑：Matt J 2021-3-30
Your criterion for agreement is too strong:
A = fft2(gpuArray(rand(10,10,5)));
A1 = ifft2(A);
A2 = ifft(ifft(A,[],2),[],1);
>> max(abs(A1-A2),[],'all')
ans =
3.3529e-16
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Matt J
Matt J 2021-3-30
编辑：Matt J 2021-3-30
Also, if your input has conjugate symmetry, it will be beneficial to use ifft(Y,[],dim,'symmetric') .
Mojtaba Zarei
Mojtaba Zarei 2021-3-30
Yes, but it is not! Thank you for your help!

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