PRACE NPT

#include <mpi.h>

#include <math.h>

#include "mpiargs.h"

#include <stdio.h>

void twiddle( int m, int n, double **ar, double **ai )

// ---------------------------------------------------------------------

// --- 'twiddle' does a complex multiplication with the appropriate

//    twiddle factors for the elements of 'ar' & 'ai' which represent

//    the Real and Imaginary parts of a 1-D 'm*(n*nodes)' length FFT,

//    factored as a sequence of 'n*nodes' FFTs of length 'm'. 'nodes'

//    is the number of processors over which the 'm'-length FFTs are

//    distributed.

// ---------------------------------------------------------------------

{

   int    i, j, nbase;

   double arg, fac, fr, fi, temp;

// ---------------------------------------------------------------------

   fac   = 8.0*atan( 1.0 )/(m*n*nodes);

   nbase = me*m;

   for( i = 0; i < m; i++ ) {

      for( j = 0; j < n; j++ ) {

         arg       = ( j*( nbase + i ) )*fac;

         fr        = cos( arg );

         fi        = sin( arg );

//printf( "me =%2d; i =%2d; j =%2d; fr =%7.3f; fi =%7.3f\n", me, i, j, fr, fi );

         temp      = ar[i][j]*fr - ai[i][j]*fi;

         ai[i][j]  = ar[i][j]*fi + ai[i][j]*fr;

         ar[i][j]  = temp;

      }

   }

}