#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <fftw.h>
/*
FFTW_MEASURE: find the optimal plan by actually computing several FFTs
FFTW_ESTIMATE: do not run any FFT and provide a "reasonable" plan
FFTW_OUT_OF_PLACE: a plan assumes that the in and out are distinct
FFTW_IN_PLACE: a plan assumes that the in and out are same
*/
/* command line argument must be size (N) ! */
int main(int argc, char *argv[]) {
int N=0,i,j;
fftw_complex *in,*out;
fftw_plan fwd_plan, bck_plan;
double err=0.0;
/* get N from the argument, make sure it is greater than zero */
if(argc>1) { N = atoi(argv[1]); }
else { printf("usage: %s N\n\t N = length of vector\n",argv[0]); }
if(N<1) { printf("\tN = %d ... exiting\n",N); exit(1); }
/* allocate memory for the input and output arrays,
initialize input array to (1.,0.) */
in = (fftw_complex *)malloc(N*sizeof(fftw_complex));
out = (fftw_complex *)malloc(N*sizeof(fftw_complex));
printf("input values:\n");
for (i=0; i<N; ++i)
{ in[i].re = 1.0;
in[i].im = 0.0;
printf("in %.3e %.3e \n",in[i].re, in[i].im);
}
printf("\n");
/* construct plans */
fwd_plan = fftw_create_plan(N, FFTW_FORWARD, FFTW_ESTIMATE);
bck_plan = fftw_create_plan(N, FFTW_BACKWARD, FFTW_ESTIMATE);
printf("Forward FFTW plan :\n");
fftw_fprint_plan(stdout,fwd_plan);
printf("\n");
printf("Backward FFTW plan :\n");
fftw_fprint_plan(stdout,bck_plan);
printf("\n");
/* do forward fft */
fftw_one(fwd_plan, in, out);
printf("FFT output:\n");
for (i=0; i<N; ++i) { printf("out %.3e %.3e \n",out[i].re, out[i].im); }
printf("\n");
/* do backward fft */
fftw_one(bck_plan, out, in);
printf("Backward FFT output:\n");
for (i=0; i<N; ++i) { printf("inv %.3e %.3e \n",in[i].re, in[i].im); }
printf("\n");
for (i=0; i<N; ++i) {
err = pow((N-in[i].re),2.0) + pow(in[i].im,2.0);
if(err > 0.0) printf("ERROR:: index=%d err=%.3e \n", i,err);
}
fftw_destroy_plan(fwd_plan);
fftw_destroy_plan(bck_plan);
return 0;
}
