c_reassign.c

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/*!
  \file cluster/c_reassign.c
  
  \brief Cluster library - Reassign cluster
  
  (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 ?

  \param C pointer to Cluster structure
  \param interrupted

  \return number of changes
*/
int I_cluster_reassign(struct Cluster *C, int *interrupted)
{
    double min, d, z;
    double q;
    int c, np;
    int old;
    int p, band, class;
    int changes;
    int first;

    changes = 0;
    for (c = 0; c < C->nclasses; c++) {
        C->countdiff[c] = 0;
        for (band = 0; band < C->nbands; band++)
            C->sumdiff[band][c] = 0;
    }

    min = HUGE_VAL;
    class = 0;
    for (p = 0; p < C->npoints; p++) {
        if (*interrupted)
            return 0;
        if (C->class[p] < 0)    /* point to be ignored */
            continue;

        /* find minimum distance to center of all classes */
        first = 1;
        for (c = 0; c < C->nclasses; c++) {
            d = 0;
            np = C->count[c];
            if (np == 0)
                continue;
            for (band = 0; band < C->nbands; band++) {
                z = C->points[band][p] * np - C->sum[band][c];
                d += z * z;
            }
            d /= (np * np);

            if (first || (d < min)) {
                class = c;
                min = d;
                first = 0;
            }
        }

        if (C->class[p] != class) {
            old = C->class[p];
            C->class[p] = class;
            changes++;

            C->countdiff[class]++;
            C->countdiff[old]--;

            for (band = 0; band < C->nbands; band++) {
                q = C->points[band][p];
                C->sumdiff[band][class] += q;
                C->sumdiff[band][old] -= q;
            }
        }
    }

    if (changes) {
        for (c = 0; c < C->nclasses; c++) {
            C->count[c] += C->countdiff[c];
            for (band = 0; band < C->nbands; band++)
                C->sum[band][c] += C->sumdiff[band][c];
        }
    }

    return changes;
}