scg_utils.c

/*
 *  SCGlib : A C library for the spectral coarse graining of matrices
 *  as described in the paper: Shrinking Matrices while preserving their
 *  eigenpairs with Application to the Spectral Coarse Graining of Graphs.
 *  Preprint available at <http://people.epfl.ch/david.morton>
 *
 *  Copyright (C) 2008 David Morton de Lachapelle <david.morton@a3.epfl.ch>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 *  02110-1301 USA
 *
 *  DESCRIPTION
 *  -----------
 *    This files contains the data structures and error handing
 *    functions used throughout the SCGlib.
 */

#include "igraph_error.h"
#include "igraph_memory.h"

#include "scg_headers.h"

/*to be used with qsort and struct ind_val arrays */
int igraph_i_compare_ind_val(const void *a, const void *b) {
    igraph_i_scg_indval_t *arg1 = (igraph_i_scg_indval_t *) a;
    igraph_i_scg_indval_t *arg2 = (igraph_i_scg_indval_t *) b;

    if ( arg1->val < arg2->val ) {
        return -1;
    } else if ( arg1->val == arg2->val ) {
        return 0;
    } else {
        return 1;
    }
}

/*to be used with qsort and struct groups*/
int igraph_i_compare_groups(const void *a, const void *b) {
    igraph_i_scg_groups_t *arg1 = (igraph_i_scg_groups_t *) a;
    igraph_i_scg_groups_t *arg2 = (igraph_i_scg_groups_t *) b;
    int i;
    for (i = 0; i < arg1->n; i++) {
        if (arg1->gr[i] > arg2->gr[i]) {
            return 1;
        } else if (arg1->gr[i] < arg2->gr[i]) {
            return -1;
        }
    }
    return 0;
}

/*to be used with qsort and real_vectors */
int igraph_i_compare_real(const void *a, const void *b) {
    igraph_real_t arg1 = * (igraph_real_t *) a;
    igraph_real_t arg2 = * (igraph_real_t *) b;

    if (arg1 < arg2) {
        return -1;
    } else if (arg1 == arg2) {
        return 0;
    } else {
        return 1;
    }
}

/*to be used with qsort and integer vectors */
int igraph_i_compare_int(const void *a, const void *b) {
    int arg1 = * (int *) a;
    int arg2 = * (int *) b;
    return (arg1 - arg2);
}

/* allocate a igraph_real_t symmetrix matrix with dimension size x size
   in vector format*/
igraph_real_t *igraph_i_real_sym_matrix(const int size)  {
    igraph_real_t *S = igraph_Calloc(size * (size + 1) / 2, igraph_real_t);
    if (!S) {
        igraph_error("allocation failure in real_sym_matrix()",
                     __FILE__, __LINE__, IGRAPH_ENOMEM);
    }
    return S;
}