Hello, I have a 2D signal (x,y) in an array, and I would like to fourier transform it along one and only one dimension, x for example. I have (nx+1) and (ny+1) points in the x and y direction respectively. the data is stored in a 1D array so that the (i,j) point is simply i + j*(nx+1) I think that the advanced interface should be good for my problem, but I don't understand some of the parameters required to make the plan. fftw_plan fftw_plan_many_dft_r2c(int rank, const int *n, int howmany, double *in, const int *inembed, int istride, int idist, fftw_complex *out, const int *onembed, int ostride, int odist, unsigned flags); int rank : 1 const int *n; I think the only element n[0] is the logical size of the array, so I would say n[0] = nx int howmany; is the number of transform, since I want the FFT along the x direction, there is ny+1 FFT to compute, so howmany=ny+1 double *in; this is my input array, I'm not sure, should I give all (nx+1)(ny+1) points to the planner, or only (nx)(ny+1) (because the (nx+1)th point is the same as the first one.) const int *inembed; What is the difference between this parameter and *n ? should it be nx+1 ? nx ? int stride; I think this one is 1 in my case. int idist; And this one should be nx+1 since I want the fourier transform along x, i.e. along each line of nx+1 points. fftw_complex *out; In my case it should be an array of (nx/2+1)*(ny+1) fftw_complex, right ? const int *onembed; nx/2+1 ? int ostride; 1 I think int odist; nx/2+1 I think ? unsigned flag; ok I choose what I want here... Thanks for telling me where I'm wrong :) Nico

# fftw 1D transform of 2D signal

Started by ●April 2, 2008

Reply by ●April 2, 20082008-04-02

On Apr 2, 3:52 am, Nico <nicolas.au...@free.fr> wrote:> I have a 2D signal (x,y) in an array, and I would like to fourier > transform it along one and only one dimension, x for example. > ....It looks fine to me; I'm not sure what your question is or why you think it is wrong. Why not just try it for a small sample dataset? (Note that the nembed parameters are really only important for one- dimensional transforms, for cases where you are performing a multi- dimensional transform of a portion of a multi-dimensional array. Here, your transforms are 1d so these parameters are ignored anyway and you could just pass NULL.) Regards, Steven G. Johnson