#include "geostat.h"


#include <math.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.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;
    
    /*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;
            }
        }
    }
}