EXEMPLE D'UTILISATION DE LA TRANSFORMEE DE FOURIER DISCRETE

import java.io.*;
import java.lang.*;

class DFT 
{   static  int NMAX = 128; 
    static  int MMAX = 8;

static double [] fr = new double[NMAX]; 
static double [] fi = new double[NMAX];
static double [] gr = new double[NMAX];
static double [] gi = new double[NMAX];

static void dft(double [] fr, double [] fi,double [] gr,double [] gi, int n) 
{


int i,j;
double pi,x,q;

pi = 4*Math.atan(1);
x  = 2*pi/n;

for (i = 0; i < n; ++i)
  {
  gr[i] = 0;
  gi[i] = 0;
  for (j = 0; j < n; ++j)
    {
    q = x*j*i;
    gr[i] = gr[i]+fr[j]*Math.cos(q)+fi[j]*Math.sin(q);
    gi[i] = gi[i]+fi[j]*Math.cos(q)-fr[j]*Math.sin(q);
    }
  }
}


public static void main( String argv[] ) { 

int i,n,m;
double f0,h,rn,x;
//double fr[],fi[],gr[],gi[];
double [] fr = new double[NMAX];
double [] fi = new double[NMAX];
double [] gr = new double[NMAX];
double [] gi = new double[NMAX];
n = NMAX;
m = MMAX;
h = 1.0/(n-1);
rn = n;
f0 = 1/Math.sqrt(rn);

for (i = 0; i < n; ++i)
  {
  x = h*i;
  fr[i] = x*(1-x);
  fi[i] = 0;
  }
dft (fr,fi,gr,gi,n);
for (i = 0; i < n; ++i)
  {
  gr[i] = f0*gr[i];
  gi[i] = f0*gi[i];
  }

/* execution de la transformee inverse */

for (i = 0; i < n; ++i)
  {
  gi[i] = -gi[i];
  }
dft (gr,gi,fr,fi,n);
for (i = 0; i < n; ++i)
  {
  fr[i] =  f0*fr[i];
  fi[i] = -f0*fi[i];
  if (i == 0 || i%m == 0)
    {
    x = h*i;
    System.out.println(x + " " + fr[i] );
    }
  }
}
}