matrix.c

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/*!
 * \author
 * Lubos Mitas (original program and various modifications)
 *
 * \author
 * H. Mitasova,
 * I. Kosinovsky, D. Gerdes,
 * D. McCauley
 * (GRASS4.1 version of the program and GRASS4.2 modifications)
 *
 * \author
 * L. Mitas,
 * H. Mitasova,
 * I. Kosinovsky,
 * D.Gerdes,
 * D. McCauley
 * (1993, 1995)
 *
 * \author modified by McCauley in August 1995
 * \author modified by Mitasova in August 1995, Nov. 1996
 *
 * SPDX-FileCopyrightText: 1993-1996 Lubos Mitas
 * SPDX-FileCopyrightText: GRASS Development Team
 * SPDX-License-Identifier: GPL-2.0-or-later
 */
 
#include <stdio.h>
#include <math.h>
#include <unistd.h>
#include <grass/gis.h>
#include <grass/interpf.h>
#include <grass/gmath.h>
 
int IL_matrix_create(struct interp_params *params,
                     struct triple *points, /* points for interpolation */
                     int n_points,          /* number of points */
                     double **matrix,       /* matrix */
                     int *indx)
{
    static double *A = NULL;
 
    if (!A) {
        if (!(A = G_alloc_vector((params->KMAX2 + 2) * (params->KMAX2 + 2) +
                                 1))) {
            fprintf(stderr, "Cannot allocate memory for A\n");
            return -1;
        }
    }
    return IL_matrix_create_alloc(params, points, n_points, matrix, indx, A);
}
 
/*!
 * \brief Creates system of linear equations from interpolated points
 *
 * Creates system of linear equations represented by matrix using given
 * points and interpolating function interp()
 *
 * \param params struct interp_params *
 * \param points points for interpolation as struct triple
 * \param n_points number of points
 * \param[out] matrix the matrix
 * \param indx
 *
 * \return -1 on failure, 1 on success
 */
int IL_matrix_create_alloc(struct interp_params *params,
                           struct triple *points, /* points for interpolation */
                           int n_points,          /* number of points */
                           double **matrix,       /* matrix */
                           int *indx, double *A
                           /* temporary matrix unique for all threads */)
{
    double xx, yy;
    double rfsta2, r;
    double d;
    int n1, k1, k2, k, i1, l, m, i, j;
    double fstar2 = params->fi * params->fi / 4.;
    double RO, amaxa;
    double rsin = 0, rcos = 0, teta,
           scale = 0; /*anisotropy parameters - added by JH 2002 */
    double xxr, yyr;
 
    if (params->theta) {
        teta = params->theta * (M_PI / 180); /* deg to rad */
        rsin = sin(teta);
        rcos = cos(teta);
    }
    if (params->scalex)
        scale = params->scalex;
 
    n1 = n_points + 1;
 
    /*
       C      GENERATION OF MATRIX
       C      FIRST COLUMN
     */
    A[1] = 0.;
    for (k = 1; k <= n_points; k++) {
        i1 = k + 1;
        A[i1] = 1.;
    }
    /*
       C      OTHER COLUMNS
     */
    RO = -params->rsm;
    /* fprintf (stderr, "sm[%d] = %f,  ro=%f\n", 1, points[1].smooth, RO); */
    for (k = 1; k <= n_points; k++) {
        k1 = k * n1 + 1;
        k2 = k + 1;
        i1 = k1 + k;
        if (params->rsm < 0.) {        /*indicates variable smoothing */
            A[i1] = -points[k - 1].sm; /* added by Mitasova nov. 96 */
            /* G_debug(5, "sm[%d]=%f, a=%f", k, points[k-1].sm, A[i1]); */
        }
        else {
            A[i1] = RO; /* constant smoothing */
        }
        /* if (i1 == 100) fprintf (stderr,i "A[%d] = %f\n", i1, A[i1]); */
 
        /* A[i1] = RO; */
        for (l = k2; l <= n_points; l++) {
            xx = points[k - 1].x - points[l - 1].x;
            yy = points[k - 1].y - points[l - 1].y;
 
            if ((params->theta) && (params->scalex)) {
                /* re run anisotropy */
                xxr = xx * rcos + yy * rsin;
                yyr = yy * rcos - xx * rsin;
                xx = xxr;
                yy = yyr;
                r = scale * xx * xx + yy * yy;
                rfsta2 = fstar2 * (scale * xx * xx + yy * yy);
            }
            else {
                r = xx * xx + yy * yy;
                rfsta2 = fstar2 * (xx * xx + yy * yy);
            }
 
            if (rfsta2 == 0.) {
                fprintf(stderr, "ident. points in segm.\n");
                fprintf(stderr, "x[%d]=%f, x[%d]=%f, y[%d]=%f, y[%d]=%f\n",
                        k - 1, points[k - 1].x, l - 1, points[l - 1].x, k - 1,
                        points[k - 1].y, l - 1, points[l - 1].y);
                return -1;
            }
            i1 = k1 + l;
            A[i1] = params->interp(r, params->fi);
        }
    }
 
    /* C       SYMMETRISATION */
    amaxa = 1.;
    for (k = 1; k <= n1; k++) {
        k1 = (k - 1) * n1;
        k2 = k + 1;
        for (l = k2; l <= n1; l++) {
            m = (l - 1) * n1 + k;
            A[m] = A[k1 + l];
            amaxa = amax1(A[m], amaxa);
        }
    }
    m = 0;
    for (i = 0; i <= n_points; i++) {
        for (j = 0; j <= n_points; j++) {
            m++;
            matrix[i][j] = A[m];
        }
    }
 
    G_debug(3, "calling G_ludcmp()  n=%d indx=%d", n_points, *indx);
    if (G_ludcmp(matrix, n_points + 1, indx, &d) <= 0) {
        /* find the inverse of the matrix */
        fprintf(stderr, "G_ludcmp() failed! n=%d  d=%.2f\n", n_points, d);
        return -1;
    }
 
    /* G_free_vector(A); */
    return 1;
}