c_means.c

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/*!
   \file cluster/c_means.c
 
   \brief Cluster library - Means value
 
   (C) 2001-2009 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.
 
   \author Original author CERL
 */
 
#include <math.h>
#include <grass/cluster.h>
 
/*!
   \brief Calculate means value
 
   \param C pointer to Cluster structure
 
   \return 0
 */
int I_cluster_means(struct Cluster *C)
{
    int band;
    int class;
    double m, v; /* m=mean, v=variance then std dev */
    double s;
 
    G_debug(3, "I_cluster_means(nbands=%d,nclasses=%d)", C->nbands,
            C->nclasses);
 
    for (band = 0; band < C->nbands; band++) {
        s = C->band_sum[band];
        m = s / C->npoints;
        v = C->band_sum2[band] - s * m;
        v = sqrt(v / (C->npoints - 1));
        for (class = 0; class < C->nclasses; class++)
            C->mean[band][class] = m;
        if (C->nclasses > 1)
            for (class = 0; class < C->nclasses; class++)
                C->mean[band][class] +=
                    ((2.0 * class) / (C->nclasses - 1) - 1.0) * v;
    }
 
    return 0;
}