static int Choleski_decompose(double *X, double *L, int n, int lapack){ int i,j,error_code; char upper = 'U'; for (i=0; i < n; i++){ for (j=0; j < n; j++){ if (i > j) L[j*n+i] = 0.0; else { L[j*n+i] = X[j*n + i]; } } } #if 0 if (!lapack){ dpofa_(L,&n,&n,&error_code); } else { dpotrf_(&upper,&n,L,&n,&error_code); } #endif error_code = LAPACKE_dpotrf( LAPACK_COL_MAJOR, upper, n, L, n ); return error_code; }
void PGSRF( GeomSolid * geounit, GrGeomSolid *gr_geounit, Vector * field, RFCondData * cdata) { /*-----------------* * Local variables * *-----------------*/ PFModule *this_module = ThisPFModule; PublicXtra *public_xtra = (PublicXtra*)PFModulePublicXtra(this_module); InstanceXtra *instance_xtra = (InstanceXtra*)PFModuleInstanceXtra(this_module); /* Input parameters (see PGSRFNewPublicXtra() below) */ double lambdaX = (public_xtra->lambdaX); double lambdaY = (public_xtra->lambdaY); double lambdaZ = (public_xtra->lambdaZ); double mean = (public_xtra->mean); double sigma = (public_xtra->sigma); int dist_type = (public_xtra->dist_type); double low_cutoff = (public_xtra->low_cutoff); double high_cutoff = (public_xtra->high_cutoff); int max_search_rad = (public_xtra->max_search_rad); int max_npts = (public_xtra->max_npts); int max_cpts = (public_xtra->max_cpts); Vector *tmpRF = NULL; /* Conditioning data */ int nc = (cdata->nc); double *x = (cdata->x); double *y = (cdata->y); double *z = (cdata->z); double *v = (cdata->v); /* Grid parameters */ Grid *grid = (instance_xtra->grid); Subgrid *subgrid; Subvector *sub_field; Subvector *sub_tmpRF; int NX, NY, NZ; /* Subgrid parameters */ int nx, ny, nz; double dx, dy, dz; int nx_v, ny_v, nz_v; int nx_v2, ny_v2, nz_v2; int nxG, nyG, nzG; /* Counters, indices, flags */ int gridloop; int i, j, k, n, m; int ii, jj, kk; int i2, j2, k2; int imin, jmin, kmin; int rpx, rpy, rpz; int npts; int index1, index2, index3; /* Spatial variables */ double *fieldp; double *tmpRFp; int iLx, iLy, iLz; /* Correlation length in terms of grid points */ int iLxp1, iLyp1, iLzp1; /* One more than each of the above */ int nLx, nLy, nLz; /* Size of correlation neighborhood in grid pts. */ int iLxyz; /* iLxyz = iLx*iLy*iLz */ int nLxyz; /* nLxyz = nLx*nLy*nLz */ int ix, iy, iz; int ref; int ix2, iy2, iz2; int i_search, j_search, k_search; int ci_search, cj_search, ck_search; double X0, Y0, Z0; /* Variables used in kriging algorithm */ double cmean, csigma; /* Conditional mean and std. dev. from kriging */ double A; double *A_sub; /* Sub-covariance matrix for external cond pts */ double *A11; /* Submatrix; note that A11 is 1-dim */ double **A12, **A21, **A22;/* Submatrices for external conditioning data */ double **M; /* Used as a temporary matrix */ double *b; /* Covariance vector for conditioning points */ double *b_tmp, *b2; double *w, *w_tmp; /* Solution vector to Aw=b */ int *ixx, *iyy, *izz; double *value; int di, dj, dk; double uni, gau; double ***cov; int ierr; /* Conditioning data variables */ int cpts; /* N cond pts for a single simulated node */ double *cval; /* Values for cond data for single node */ /* Communications */ VectorUpdateCommHandle *handle; int update_mode; /* Miscellaneous variables */ int **rand_path; char ***marker; int p, r, modulus; double a1, a2, a3; double cx, cy, cz; double sum; // FIXME Shouldn't we get this from numeric_limits? double Tiny = 1.0e-12; (void)geounit; /*----------------------------------------------------------------------- * Allocate temp vectors *-----------------------------------------------------------------------*/ tmpRF = NewVectorType(instance_xtra->grid, 1, max_search_rad, vector_cell_centered); /*----------------------------------------------------------------------- * Start sequential Gaussian simulator algorithm *-----------------------------------------------------------------------*/ /* Begin timing */ BeginTiming(public_xtra->time_index); /* initialize random number generators */ SeedRand(public_xtra->seed); /* For now, we will assume that all subgrids have the same uniform spacing */ subgrid = GridSubgrid(grid, 0); dx = SubgridDX(subgrid); dy = SubgridDY(subgrid); dz = SubgridDZ(subgrid); /* Size of search neighborhood through which random path must be defined */ iLx = (int)(lambdaX / dx); iLy = (int)(lambdaY / dy); iLz = (int)(lambdaZ / dz); /* For computational efficiency, we'll limit the * size of the search neighborhood. */ if (iLx > max_search_rad) iLx = max_search_rad; if (iLy > max_search_rad) iLy = max_search_rad; if (iLz > max_search_rad) iLz = max_search_rad; iLxp1 = iLx + 1; iLyp1 = iLy + 1; iLzp1 = iLz + 1; iLxyz = iLxp1 * iLyp1 * iLzp1; /* Define the size of a correlation neighborhood */ nLx = 2 * iLx + 1; nLy = 2 * iLy + 1; nLz = 2 * iLz + 1; nLxyz = nLx * nLy * nLz; /*------------------------ * Define a random path through the points in this subgrid. * The random path generation procedure of Srivastava and * Gomez has been adopted in this subroutine. A linear * congruential generator of the form: r(i) = 5*r(i-1)+1 mod(2**n) * has a cycle length of 2**n. By choosing the smallest power of * 2 that is still larger than the total number of points to be * simulated, the method ensures that all indices will be * generated once and only once. *------------------------*/ rand_path = talloc(int*, iLxyz); for (i = 0; i < iLxyz; i++) rand_path[i] = talloc(int, 3); modulus = 2; while (modulus < iLxyz + 1) modulus *= 2; /* Compute a random starting node */ p = (int)Rand(); r = 1 + p * (iLxyz - 1); k = (r - 1) / (iLxp1 * iLyp1); j = (r - 1 - iLxp1 * iLyp1 * k) / iLxp1; i = (r - 1) - (k * iLyp1 + j) * iLxp1; rand_path[0][2] = k; rand_path[0][1] = j; rand_path[0][0] = i; /* Determine the next nodes */ for (n = 1; n < iLxyz; n++) { r = (5 * r + 1) % modulus; while ((r < 1) || (r > iLxyz)) r = (5 * r + 1) % modulus; k = ((r - 1) / (iLxp1 * iLyp1)); j = (((r - 1) - iLxp1 * iLyp1 * k) / iLxp1); i = (r - 1) - (k * iLyp1 + j) * iLxp1; rand_path[n][0] = i; rand_path[n][1] = j; rand_path[n][2] = k; } /*----------------------------------------------------------------------- * Compute correlation lookup table *-----------------------------------------------------------------------*/ /* First compute a covariance lookup table */ cov = talloc(double**, nLx); for (i = 0; i < nLx; i++) { cov[i] = talloc(double*, nLy); for (j = 0; j < nLy; j++) cov[i][j] = ctalloc(double, nLz); } /* Note that in the construction of the covariance matrix * the max_search_rad is not used. Covariance depends upon * the correlation lengths, lambdaX/Y/Z, and the grid spacing. * The max_search_rad can be longer or shorter than the correlation * lengths. The bigger the search radius, the more accurately * the random field will match the correlation structure of the * covariance function. But the run time will increase greatly * as max_search_rad gets bigger because of the kriging matrix * that must be solved (see below). */ cx = 0.0; cy = 0.0; cz = 0.0; if (lambdaX != 0.0) cx = dx * dx / (lambdaX * lambdaX); if (lambdaY != 0.0) cy = dy * dy / (lambdaY * lambdaY); if (lambdaZ != 0.0) cz = dz * dz / (lambdaZ * lambdaZ); for (k = 0; k < nLz; k++) for (j = 0; j < nLy; j++) for (i = 0; i < nLx; i++) { a1 = i * i * cx; a2 = j * j * cy; a3 = k * k * cz; cov[i][j][k] = exp(-sqrt(a1 + a2 + a3)); } /* Allocate memory for variables that will be used in kriging */ A11 = ctalloc(double, nLxyz * nLxyz); A_sub = ctalloc(double, nLxyz * nLxyz); A12 = ctalloc(double*, nLxyz); A21 = ctalloc(double*, nLxyz); A22 = ctalloc(double*, nLxyz); M = ctalloc(double*, nLxyz); for (i = 0; i < nLxyz; i++) { A12[i] = ctalloc(double, nLxyz); A21[i] = ctalloc(double, nLxyz); A22[i] = ctalloc(double, nLxyz); M[i] = ctalloc(double, nLxyz); } b = ctalloc(double, nLxyz); b2 = ctalloc(double, nLxyz); b_tmp = ctalloc(double, nLxyz); w = ctalloc(double, nLxyz); w_tmp = ctalloc(double, nLxyz); value = ctalloc(double, nLxyz); cval = ctalloc(double, nLxyz); ixx = ctalloc(int, nLxyz); iyy = ctalloc(int, nLxyz); izz = ctalloc(int, nLxyz); /* Allocate space for the "marker" used to keep track of which * points in a representative correlation box have been simulated * already. */ marker = talloc(char**, (3 * iLx + 1)); marker += iLx; for (i = -iLx; i <= 2 * iLx; i++) { marker[i] = talloc(char*, (3 * iLy + 1)); marker[i] += iLy; for (j = -iLy; j <= 2 * iLy; j++) { marker[i][j] = ctalloc(char, (3 * iLz + 1)); marker[i][j] += iLz; for (k = -iLz; k <= 2 * iLz; k++) marker[i][j][k] = 0; } } /* Convert the cutoff values to a gaussian if they're lognormal on input */ if ((dist_type == 1) || (dist_type == 3)) { if (low_cutoff <= 0.0) { low_cutoff = Tiny; } else { low_cutoff = (log(low_cutoff / mean)) / sigma; } if (high_cutoff <= 0.0) { high_cutoff = DBL_MAX; } else { high_cutoff = (log(high_cutoff / mean)) / sigma; } } /*-------------------------------------------------------------------- * Start pGs algorithm *--------------------------------------------------------------------*/ for (gridloop = 0; gridloop < GridNumSubgrids(grid); gridloop++) { subgrid = GridSubgrid(grid, gridloop); sub_tmpRF = VectorSubvector(tmpRF, gridloop); sub_field = VectorSubvector(field, gridloop); tmpRFp = SubvectorData(sub_tmpRF); fieldp = SubvectorData(sub_field); X0 = RealSpaceX(0, SubgridRX(subgrid)); Y0 = RealSpaceY(0, SubgridRY(subgrid)); Z0 = RealSpaceZ(0, SubgridRZ(subgrid)); ix = SubgridIX(subgrid); iy = SubgridIY(subgrid); iz = SubgridIZ(subgrid); nx = SubgridNX(subgrid); ny = SubgridNY(subgrid); nz = SubgridNZ(subgrid); NX = ix + nx; NY = iy + ny; NZ = iz + nz; /* RDF: assume resolution is the same in all 3 directions */ ref = SubgridRX(subgrid); nx_v = SubvectorNX(sub_field); ny_v = SubvectorNY(sub_field); nz_v = SubvectorNZ(sub_field); nx_v2 = SubvectorNX(sub_tmpRF); ny_v2 = SubvectorNY(sub_tmpRF); nz_v2 = SubvectorNZ(sub_tmpRF); /* Initialize tmpRF vector */ GrGeomInLoop(i, j, k, gr_geounit, ref, ix, iy, iz, nx, ny, nz, { index2 = SubvectorEltIndex(sub_tmpRF, i, j, k); tmpRFp[index2] = 0.0; }); /* Convert conditioning data to N(0,1) distribution if * it's assumed to be lognormal. Then copy it into tmpRFp */ if ((dist_type == 1) || (dist_type == 3)) { for (n = 0; n < nc; n++) { i = (int)((x[n] - X0) / dx + 0.5); j = (int)((y[n] - Y0) / dy + 0.5); k = (int)((z[n] - Z0) / dz + 0.5); if ((ix - max_search_rad <= i && i <= ix + nx + max_search_rad) && (iy - max_search_rad <= j && j <= iy + ny + max_search_rad) && (iz - max_search_rad <= k && k <= iz + nz + max_search_rad)) { index2 = SubvectorEltIndex(sub_tmpRF, i, j, k); if (v[n] <= 0.0) tmpRFp[index2] = Tiny; else tmpRFp[index2] = (log(v[n] / mean)) / sigma; } } } /* Otherwise, shift data to N(0,1) distribution */ else { for (n = 0; n < nc; n++) { i = (int)((x[n] - X0) / dx + 0.5); j = (int)((y[n] - Y0) / dy + 0.5); k = (int)((z[n] - Z0) / dz + 0.5); if ((ix - max_search_rad <= i && i <= ix + nx + max_search_rad) && (iy - max_search_rad <= j && j <= iy + ny + max_search_rad) && (iz - max_search_rad <= k && k <= iz + nz + max_search_rad)) { index2 = SubvectorEltIndex(sub_tmpRF, i, j, k); tmpRFp[index2] = (v[n] - mean) / sigma; } } } /* Set the search radii in each direction. If the maximum * number of points in a neighborhood is exceeded, these limits * will be reduced. */ i_search = iLx; j_search = iLy; k_search = iLz; /* Compute values at all points using all templates */ for (n = 0; n < iLxyz; n++) { /* Update the ghost layer before proceeding */ if (n > 0) { /* First reset max_search_radius */ max_search_rad = i_search; if (j_search > max_search_rad) max_search_rad = j_search; if (k_search > max_search_rad) max_search_rad = k_search; /* Reset the comm package based on the new max_search_radius */ if (max_search_rad == 1) update_mode = VectorUpdatePGS1; else if (max_search_rad == 2) update_mode = VectorUpdatePGS2; else if (max_search_rad == 3) update_mode = VectorUpdatePGS3; else update_mode = VectorUpdatePGS4; handle = InitVectorUpdate(tmpRF, update_mode); FinalizeVectorUpdate(handle); } rpx = rand_path[n][0]; rpy = rand_path[n][1]; rpz = rand_path[n][2]; ix2 = rpx; while (ix2 < ix) ix2 += iLxp1; iy2 = rpy; while (iy2 < iy) iy2 += iLyp1; iz2 = rpz; while (iz2 < iz) iz2 += iLzp1; /* This if clause checks to see if there are, in fact, * any points at all in this subgrid, for this * particular region. Note that each value of n in the * above n-loop corresponds to a different region. */ if ((ix2 < ix + nx) && (iy2 < iy + ny) && (iz2 < iz + nz)) { /* * Construct the input matrix and vector for kriging, * solve the linear system, and compute csigma. * These depend only on the spatial distribution of * conditioning data, not on the actual values of * the data. Only the conditional mean (cmean) depends * on actual values, so it must be computed for every * point. Thus, it's found within the pgs_Boxloop below. * The size of the linear system that must be solved here * will be no larger than (2r+1)^3, where r=max_search_rad. * It is clear from this why it is necessary to limit * the size of the search radius. */ /* Here the marker array indicates which points within * the search radius have been simulated already. This * spatial pattern of conditioning points will be the * same for every point in the current template. Thus, * this system can be solved once *outside* of the * GrGeomInLoop2 below. */ npts = 9999; while (npts > max_npts) { m = 0; /* Count the number of points in search ellipse */ for (k = rpz - k_search; k <= rpz + k_search; k++) for (j = rpy - j_search; j <= rpy + j_search; j++) for (i = rpx - i_search; i <= rpx + i_search; i++) { if (marker[i][j][k]) { ixx[m] = i; iyy[m] = j; izz[m++] = k; } } npts = m; /* If npts is too large, reduce the size of the * search ellipse one axis at a time. */ if (npts > max_npts) { /* If i_search is the biggest, reduce it by one. */ if ((i_search >= j_search) && (i_search >= k_search)) { i_search--; } /* Or, if j_search is the biggest, reduce it by one. */ else if ((j_search >= i_search) && (j_search >= k_search)) { j_search--; } /* Otherwise, reduce k_search by one. */ else { k_search--; } } } m = 0; for (j = 0; j < npts; j++) { di = abs(rpx - ixx[j]); dj = abs(rpy - iyy[j]); dk = abs(rpz - izz[j]); b[j] = cov[di][dj][dk]; for (i = 0; i < npts; i++) { di = abs(ixx[i] - ixx[j]); dj = abs(iyy[i] - iyy[j]); dk = abs(izz[i] - izz[j]); A11[m++] = cov[di][dj][dk]; } } /* Solve the linear system */ for (i = 0; i < npts; i++) w[i] = b[i]; if (npts > 0) { dpofa_(A11, &npts, &npts, &ierr); dposl_(A11, &npts, &npts, w); } /* Compute the conditional standard deviation for the RV * to be simulated. */ csigma = 0.0; for (i = 0; i < npts; i++) csigma += w[i] * b[i]; csigma = sqrt(cov[0][0][0] - csigma); /* The following loop hits every point in the current * region. That is, it skips by max_search_rad+1 * through the subgrid. In this way, all the points * in this loop may simulated simultaneously; each is * outside the search radius of all the others. */ nxG = (nx + ix); nyG = (ny + iy); nzG = (nz + iz); for (k = iz2; k < nzG; k += iLzp1) for (j = iy2; j < nyG; j += iLyp1) for (i = ix2; i < nxG; i += iLxp1) { index1 = SubvectorEltIndex(sub_field, i, j, k); index2 = SubvectorEltIndex(sub_tmpRF, i, j, k); /* Only simulate points in this geounit and that don't * already have a value. If a node already has a value, * it was assigned as external conditioning data, * so we don't need to simulate it. */ if (fabs(tmpRFp[index2]) < Tiny) { /* Condition the random variable */ m = 0; cpts = 0; for (kk = -k_search; kk <= k_search; kk++) for (jj = -j_search; jj <= j_search; jj++) for (ii = -i_search; ii <= i_search; ii++) { value[m] = 0.0; index3 = SubvectorEltIndex(sub_tmpRF, i + ii, j + jj, k + kk); if (marker[ii + rpx][jj + rpy][kk + rpz]) { value[m++] = tmpRFp[index3]; } /* In this case, there is a value at this point, * but it wasn't simulated yet (as indicated by the * fact that the marker has no place for it). Thus, * it must be external conditioning data. */ else if (fabs(tmpRFp[index3]) > Tiny) { ixx[npts + cpts] = rpx + ii; iyy[npts + cpts] = rpy + jj; izz[npts + cpts] = rpz + kk; cval[cpts++] = tmpRFp[index3]; } } /* If cpts is too large, reduce the size of the * search neighborhood, one axis at a time. */ /* Define the size of the search neighborhood */ ci_search = i_search; cj_search = j_search; ck_search = k_search; while (cpts > max_cpts) { /* If ci_search is the biggest, reduce it by one. */ if ((ci_search >= cj_search) && (ci_search >= ck_search)) ci_search--; /* Or, if cj_search is the biggest, reduce it by one. */ else if ((cj_search >= ci_search) && (cj_search >= ck_search)) cj_search--; /* Otherwise, reduce ck_search by one. */ else ck_search--; /* Now recount the conditioning data points */ m = 0; cpts = 0; for (kk = -ck_search; kk <= ck_search; kk++) for (jj = -cj_search; jj <= cj_search; jj++) for (ii = -ci_search; ii <= ci_search; ii++) { index3 = SubvectorEltIndex(sub_tmpRF, i + ii, j + jj, k + kk); if (!(marker[rpx + ii][rpy + jj][rpz + kk]) && (fabs(tmpRFp[index3]) > Tiny)) { ixx[npts + cpts] = rpx + ii; iyy[npts + cpts] = rpy + jj; izz[npts + cpts] = rpz + kk; cval[cpts++] = tmpRFp[index3]; } } } for (i2 = 0; i2 < npts; i2++) w_tmp[i2] = w[i2]; /*-------------------------------------------------- * Conditioning to external data is done here. *--------------------------------------------------*/ if (cpts > 0) { /* Compute the submatrices */ for (j2 = 0; j2 < npts + cpts; j2++) { di = abs(rpx - ixx[j2]); dj = abs(rpy - iyy[j2]); dk = abs(rpz - izz[j2]); b[j2] = cov[di][dj][dk]; for (i2 = 0; i2 < npts + cpts; i2++) { di = abs(ixx[i2] - ixx[j2]); dj = abs(iyy[i2] - iyy[j2]); dk = abs(izz[i2] - izz[j2]); A = cov[di][dj][dk]; if (i2 < npts && j2 >= npts) A12[i2][j2 - npts] = A; if (i2 >= npts && j2 < npts) A21[i2 - npts][j2] = A; if (i2 >= npts && j2 >= npts) A22[i2 - npts][j2 - npts] = A; } } /* Compute b2' = b2 - A21 * A11_inv * b1 and augment b1 */ for (i2 = 0; i2 < cpts; i2++) b2[i2] = b[i2 + npts]; for (i2 = 0; i2 < npts; i2++) b_tmp[i2] = b[i2]; dposl_(A11, &npts, &npts, b_tmp); for (i2 = 0; i2 < cpts; i2++) { sum = 0.0; for (j2 = 0; j2 < npts; j2++) { sum += A21[i2][j2] * b_tmp[j2]; } b2[i2] -= sum; } for (i2 = 0; i2 < cpts; i2++) b[i2 + npts] = b2[i2]; /* Compute A22' = A22 - A21 * A11_inv * A12 */ for (j2 = 0; j2 < cpts; j2++) for (i2 = 0; i2 < npts; i2++) M[j2][i2] = A12[i2][j2]; if (npts > 0) { for (i2 = 0; i2 < cpts; i2++) dposl_(A11, &npts, &npts, M[i2]); } for (j2 = 0; j2 < cpts; j2++) for (i2 = 0; i2 < cpts; i2++) { sum = 0.0; for (k2 = 0; k2 < npts; k2++) sum += A21[i2][k2] * M[j2][k2]; A22[i2][j2] -= sum; } m = 0; for (j2 = 0; j2 < cpts; j2++) for (i2 = 0; i2 < cpts; i2++) A_sub[m++] = A22[i2][j2]; /* Compute x2 where A22*x2 = b2' */ dpofa_(A_sub, &cpts, &cpts, &ierr); dposl_(A_sub, &cpts, &cpts, b2); /* Compute w_tmp where A11*w_tmp = (b1 - A12*b2) */ if (npts > 0) { for (i2 = 0; i2 < npts; i2++) { sum = 0.0; for (k2 = 0; k2 < cpts; k2++) sum += A12[i2][k2] * b2[k2]; w_tmp[i2] = b[i2] - sum; } dposl_(A11, &npts, &npts, w_tmp); } /* Fill in the rest of w_tmp with b2 */ for (i2 = npts; i2 < npts + cpts; i2++) { w_tmp[i2] = b2[i2]; value[i2] = cval[i2 - npts]; } /* Recompute csigma */ csigma = 0.0; for (i2 = 0; i2 < npts + cpts; i2++) csigma += w_tmp[i2] * b[i2]; csigma = sqrt(cov[0][0][0] - csigma); } /*-------------------------------------------------- * End of external conditioning *--------------------------------------------------*/ cmean = 0.0; for (m = 0; m < npts + cpts; m++) cmean += w_tmp[m] * value[m]; /* uni = fieldp[index1]; */ uni = Rand(); gauinv_(&uni, &gau, &ierr); tmpRFp[index2] = csigma * gau + cmean; /* Cutoff tail values if required */ if (dist_type > 1) { if (tmpRFp[index2] < low_cutoff) tmpRFp[index2] = low_cutoff; if (tmpRFp[index2] > high_cutoff) tmpRFp[index2] = high_cutoff; } } /* if( abs(tmpRFp[index2]) < Tiny ) */ } /* end of triple for-loops over i,j,k */ /* Update the marker vector */ imin = rpx - iLxp1; if (imin < -iLx) imin += iLxp1; jmin = rpy - iLyp1; if (jmin < -iLy) jmin += iLyp1; kmin = rpz - iLzp1; if (kmin < -iLz) kmin += iLzp1; for (kk = kmin; kk <= 2 * iLz; kk += iLzp1) for (jj = jmin; jj <= 2 * iLy; jj += iLyp1) for (ii = imin; ii <= 2 * iLx; ii += iLxp1) { marker[ii][jj][kk] = 1; } } /* if(...) */ } /* n loop */ /* Make log-normal if requested. Note that low * and high cutoffs are already accomplished. */ if ((dist_type == 1) || (dist_type == 3)) { GrGeomInLoop(i, j, k, gr_geounit, ref, ix, iy, iz, nx, ny, nz, { index1 = SubvectorEltIndex(sub_field, i, j, k); index2 = SubvectorEltIndex(sub_tmpRF, i, j, k); fieldp[index1] = mean * exp((sigma) * tmpRFp[index2]); });