#include <stdio.h>
#include <stddef.h>
#include <string.h>
#include <stdarg.h>
#include <stdlib.h>
#include <math.h>
#include "geostat.h"

/* build_real   */
/* build a realization in the spectral domain */
/*n: vector with the number of cells along the */
/*   X, Y and Z axes for the underlying grid   */
/*   i = [0 1 2]                               */
/*   --> 0 0 0        : n will be computed and */
/*   updated as output                         */
/*   --> nx ny nz: these dimensions are used   */
/*covar: vector defining the covariance in spectral domain   */
/*realization: vector defining the real part   */
/*ireal: vector defining the i-part   */

void build_real(int n[3],int NTOT,double *covar,double *realization,double *ireal)
{
  int i,j,k,maille1;
  double temp;

  printf("build real\n");


  /*decomposition and multiplication in the spectral domain*/
  for ( k = 1; k <= n[2]; k++) {
    for (j = 1; j <= n[1]; j++) {
      for (i = 1; i <= n[0]; i++) {
	maille1 = i+(j-1+(k-1)*n[1])*n[0];
	temp = covar[maille1];
	if (temp > 0.) {
	  temp = sqrt(temp)/(double) NTOT;
	} else if (temp < 0.) {
	  temp = sqrt(-temp)/(double) NTOT;
	}
	realization[maille1] *= temp;
	ireal[maille1] *= temp;
      }
    }
  }
  
  return;
}