GPU FFT2 Discrepancies ( Different from CPU based FFT2 )

Hello, I have noticed a problem that Matlab FFT2 does not produce the same result on a GPU array as it does on a "normal" array.

The following code was used to ensure that my observation is correct.

totalDiff = 0;

for loop = 0:10000

      a = rand( [2 2] ); % Obtain random numbers

      cpuResult = fft2(a); % Calculate on CPU

      gpuResult = gather( fft2( gpuArray(a) ) ); % Calculate on GPU

      diff = sum( gpuResult(:) - cpuResult(:) ); % Calculate difference

      totalDiff = totalDiff + diff; % Get a running total of differences

end

totalDiff / 10000 %Output average change per matrix

I appreciate any feedback regarding this question: Why is this changing result being observed and can it be minimized or removed? While these values are not extremely different (differing by 1e-17 or so), I would still like to ensure an exact equality between my GPU and CPU code.

P.S. fft also has changing results based on the device used for computation; but, for my system, the matrix has to be larger than 4 x 4 to observe the difference.

Answer 1

[Ben Tordoff]

See the answer(s) to this question: why do some calculations like the fft produce different results when performed on a gpu?

[Kevin Blank]

Thank you, that answer is perfect and I'm sorry my searching never discovered it.