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Asked: 2026-05-23T19:34:35+00:00

I wrote a simple test program, where I was doing Complex to Complex FT’s

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I wrote a simple test program, where I was doing Complex to Complex FT’s and I just generated some data 1..50 and stuck it in for the real and imaginary part for each index of the array.

When I do an operation like this IFFT(FFT(A)) = A

to test them out, I am getting different results for each library.

FFTW, I have to divide the output by len(A) to get back the original A

However, doing this forward then reverse FFT with CUFFT, it looks like I have to divide by (sqrt(2)*50) to get back to the original data.

Where is this extra square root factor coming from?

according to the CUFFT documentation:
CUFFT performs un normalized FFTs; that is, performing a forward
FFT on an input data set followed by an inverse FFT on the resulting
set yields data that is equal to the input scaled by the number of
elements. Scaling either transform by the reciprocal of the size of the
data set is left for the user to perform as seen fit.

Thanks in Advance

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1 Answer

  1. Editorial Team

    This ended up being a problem with the way the absolute values of the complex number was being calculated. in the std::complex library, it was computing the distance of the vector.

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