Hi All:

I am having trouble figuring out what is the order in which CUDA returns a 1D forward FFT transform. Specifically I am looking for the Nyquist frequency.

For a real to complex forward transform, this is how FFTW returns frequencies:

[0:Nx/2 -Nx/2+1:-1]

Ofcourse CUDA takes care of the symmetry and only returns half of the frequencies in this order:

[0:Nx/2-1]

But where is the nuquist frequency?

I made a simple test for an array of size Nx=8 with inputs of

a[i]=i.

This is how FFTW returns the fft(a) in the above mentioned order:

28.0000

-4.0000 + 9.6569i

-4.0000 + 4.0000i

-4.0000 + 1.6569i

-4.0000

and this is how CUDA returns it:

28 0 i

-4+ 9.65685 i

-4+ 4 i

-4+ 1.65685 i

The next elements value in CUDA is 0, and not -4. So my question is which element of the output contains the nyquist frequency?