cuFFT of a matrix as a 1D transformation of rows or columns - cuda

Question

I could not find an example of application of cuFFT with CUDA in which the transformation of a matrix is realized as 1D transformations of rows and columns.
I have a 2048x2048 array (set as 1D of cuComplex data). With 2D transform - no problem. But now what I need is to do the transform along x, do some work on it, take inverse fft, then do the transform along y, and do another work on it, then take its inverse transform.
How exactly would the sequence of commands look like if I want to use parallel processing? Should I use cuFFTPlanMany? How? Or, perhaps, is there an example somewhere that I was not able to find?

Answer 1

In the cuFFT Library User's guide, on page 3, there is an example on how computing a number BATCH of one-dimensional DFTs of size NX. Using cufftPlan1d(&plan, NX, CUFFT_C2C, BATCH);, then cufftExecC2C will perform a number BATCH 1D FFTs of size NX. To achieve that, you have to arrange your data in a complex array of length BATCH*NX. In your case, for the transform along x, it would be BATCH=2048 and NX=2048. For the transforms along y, you have to transpose the matrix arising from previous calculations.
Your code will look like the following
#define NX 2048
#define NY 2048
int main() {
cufftHandle plan;
cufftComplex *data;
...
cudaMalloc((void**)&data, sizeof(cufftComplex)*NX*NY);
cufftPlan1d(&plan, NX, CUFFT_C2C, NY);
...
cufftExecC2C(plan, data, data, CUFFT_FORWARD);
...
// do some work
...
// make a transposition
...
cufftPlan1d(&plan, NY, CUFFT_C2C, NX);
...
cufftExecC2C(plan, data, data, CUFFT_FORWARD);
...
}