Fftw Transforms

[MADjestic]

Hi there,

I am trying to learn to handle properly the fftw library routines, more specifically fftw_plan_dft_r2c_1d (2d) real-to-complex forward and backward transforms. See the simple code – it looks like the whole thing works, however the input data of the array (0,1,2,3…9) turns into zeros after the transform. The in-place transform also results in all zeros. (I assume that forward-backward transform of arbitrary data must result in original unchanged data). Or am I missing something? Does anybody have experience with this and maybe can share a simple piece of code?

#include <cstdlib>
#include <fftw3.h>
#include <stdio.h>

using namespace std;
int main(int argc, char *argv[])
{
  fftw_plan pf, pb;
  int N=10, i, j;
fftw_complex *data, array[N];
double *data_d, array_d[N];

data = (fftw_complex*) fftw_malloc(sizeof(fftw_complex) * N);
data = array;

data_d = (double*) fftw_malloc(sizeof(fftw_complex) * N);
data_d = array_d; 

for(i=0;i<N;i++){array_d[i]=i;}

cout <<"******pointer *data_d values*********" << endl;
for(i=0;i<N;i++)cout<< data_d[i]<< endl;

cout <<"******FFT Forward transform*********" << endl;
pf = fftw_plan_dft_r2c_1d(N, data_d, data, FFTW_FORWARD); fftw_execute(pf);
for(i=0;i<N;i++)cout<< data[i]<< endl;

cout <<"*****FFT Backward transform********" << endl;
pb = fftw_plan_dft_c2r_1d(N, data, data_d, FFTW_BACKWARD); fftw_execute(pb);
for(i=0;i<N;i++)cout<< data_d[i]<< endl;

  return EXIT_SUCCESS;
}

[MADjestic]

For anybody interested - I found this link -

http://www.scs.fsu.edu/~burkardt/c_src/fftw3/fftw3.html

it apparently answers my question, nevertheless if you've got somethingto share - I'll appreciate this.

cheers.