/****************************************************************************
 *
 * MODULE:       r.covar
 *
 * AUTHOR(S):    Michael Shapiro - CERL
 *
 * PURPOSE:      Outputs a covariance/correlation matrix for
 *               user-specified raster map layer(s).
 *
 * COPYRIGHT:    (C) 2006 by the GRASS Development Team
 *
 *               This program is free software under the GNU General Public
 *               License (>=v2). Read the file COPYING that comes with GRASS
 *               for details.
 *
 ***************************************************************************/

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <grass/gis.h>
#include <grass/raster.h>
#include <grass/glocale.h>

int main(int argc, char *argv[])
{
    int nrows, ncols;
    DCELL **dcell;
    char *name;
    double *sum, **sum2;
    double count;
    double ii, jj;
    int *fd;
    int nfiles;
    int i, j;
    int row, col;
    int correlation;
    struct GModule *module;
    struct Option *maps;
    struct {
        struct Flag *r;
    } flag;

    G_gisinit(argv[0]);

    module = G_define_module();
    G_add_keyword(_("raster"));
    G_add_keyword(_("statistics"));
    module->description = _("Outputs a covariance/correlation matrix "
                            "for user-specified raster map layer(s).");

    maps = G_define_standard_option(G_OPT_R_MAPS);

    flag.r = G_define_flag();
    flag.r->key = 'r';
    flag.r->description = _("Print correlation matrix");

    if (G_parser(argc, argv))
        exit(EXIT_FAILURE);

    /* flags */
    correlation = flag.r->answer;

    /* count the number of raster maps */
    for (nfiles = 0; maps->answers[nfiles]; nfiles++)
        ;

    fd = (int *)G_malloc(nfiles * sizeof(int));
    dcell = (DCELL **)G_malloc(nfiles * sizeof(DCELL *));
    sum = (double *)G_calloc(nfiles, sizeof(double));
    sum2 = (double **)G_malloc(nfiles * sizeof(double *));
    for (i = 0; i < nfiles; i++) {
        sum2[i] = (double *)G_calloc(nfiles, sizeof(double));
        dcell[i] = Rast_allocate_d_buf();
        name = maps->answers[i];
        fd[i] = Rast_open_old(name, "");
    }

    nrows = Rast_window_rows();
    ncols = Rast_window_cols();

    G_message(_("%s: complete ... "), G_program_name());
    count = 0;
    for (row = 0; row < nrows; row++) {
        G_percent(row, nrows, 2);
        for (i = 0; i < nfiles; i++)
            Rast_get_d_row(fd[i], dcell[i], row);

        for (col = 0; col < ncols; col++) {
            /* ignore cells where any of the maps has null value */
            for (i = 0; i < nfiles; i++)
                if (Rast_is_d_null_value(&dcell[i][col]))
                    break;
            if (i != nfiles)
                continue;
            count++;
            for (i = 0; i < nfiles; i++) {
                sum[i] += dcell[i][col];
                for (j = 0; j <= i; j++)
                    sum2[j][i] += dcell[i][col] * dcell[j][col];
            }
        }
    }
    G_percent(row, nrows, 2);
    if (count <= 1.1)
        G_fatal_error(_("No non-null values"));

    fprintf(stdout, "N = %.0f\n", count);

    ii = jj = 1.0;
    for (i = 0; i < nfiles; i++) {
        if (correlation)
            ii = sqrt((sum2[i][i] - sum[i] * sum[i] / count) / (count - 1));
        for (j = 0; j <= i; j++) {
            if (correlation)
                jj = sqrt((sum2[j][j] - sum[j] * sum[j] / count) / (count - 1));
            fprintf(stdout, "%f ",
                    (sum2[j][i] - sum[i] * sum[j] / count) /
                        (ii * jj * (count - 1)));
        }
        for (j = i + 1; j < nfiles; j++) {
            if (correlation)
                jj = sqrt((sum2[j][j] - sum[j] * sum[j] / count) / (count - 1));
            fprintf(stdout, "%f ",
                    (sum2[i][j] - sum[i] * sum[j] / count) /
                        (ii * jj * (count - 1)));
        }
        fprintf(stdout, "\n");
    }
    exit(EXIT_SUCCESS);
}
