igraph/src/distances.c

/* -*- mode: C -*-  */
/* vim:set ts=4 sw=4 sts=4 et: */
/*
   IGraph library.
   Copyright (C) 2011-2012  Gabor Csardi <csardi.gabor@gmail.com>
   334 Harvard street, Cambridge, MA 02139 USA

   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

*/

#include "igraph_paths.h"
#include "igraph_datatype.h"
#include "igraph_dqueue.h"
#include "igraph_iterators.h"
#include "igraph_interrupt_internal.h"
#include "igraph_vector.h"
#include "igraph_interface.h"
#include "igraph_adjlist.h"

static int igraph_i_eccentricity(const igraph_t *graph,
                                 igraph_vector_t *res,
                                 igraph_vs_t vids,
                                 igraph_neimode_t mode,
                                 const igraph_adjlist_t *adjlist) {

    int no_of_nodes = igraph_vcount(graph);
    igraph_dqueue_long_t q;
    igraph_vit_t vit;
    igraph_vector_int_t counted;
    int i, mark = 1;
    igraph_vector_t vneis;
    igraph_vector_int_t *neis;

    IGRAPH_CHECK(igraph_dqueue_long_init(&q, 100));
    IGRAPH_FINALLY(igraph_dqueue_long_destroy, &q);

    IGRAPH_CHECK(igraph_vit_create(graph, vids, &vit));
    IGRAPH_FINALLY(igraph_vit_destroy, &vit);

    IGRAPH_CHECK(igraph_vector_int_init(&counted, no_of_nodes));
    IGRAPH_FINALLY(igraph_vector_int_destroy, &counted);

    if (!adjlist) {
        IGRAPH_VECTOR_INIT_FINALLY(&vneis, 0);
    }

    IGRAPH_CHECK(igraph_vector_resize(res, IGRAPH_VIT_SIZE(vit)));
    igraph_vector_fill(res, -1);

    for (i = 0, IGRAPH_VIT_RESET(vit);
         !IGRAPH_VIT_END(vit);
         IGRAPH_VIT_NEXT(vit), mark++, i++) {

        long int source;
        source = IGRAPH_VIT_GET(vit);
        IGRAPH_CHECK(igraph_dqueue_long_push(&q, source));
        IGRAPH_CHECK(igraph_dqueue_long_push(&q, 0));
        VECTOR(counted)[source] = mark;

        IGRAPH_ALLOW_INTERRUPTION();

        while (!igraph_dqueue_long_empty(&q)) {
            long int act = igraph_dqueue_long_pop(&q);
            long int dist = igraph_dqueue_long_pop(&q);
            int j, n;

            if (dist > VECTOR(*res)[i]) {
                VECTOR(*res)[i] = dist;
            }

            if (adjlist) {
                neis = igraph_adjlist_get(adjlist, act);
                n = (int) igraph_vector_int_size(neis);
                for (j = 0; j < n; j++) {
                    int nei = (int) VECTOR(*neis)[j];
                    if (VECTOR(counted)[nei] != mark) {
                        VECTOR(counted)[nei] = mark;
                        IGRAPH_CHECK(igraph_dqueue_long_push(&q, nei));
                        IGRAPH_CHECK(igraph_dqueue_long_push(&q, dist + 1));
                    }
                }
            } else {
                IGRAPH_CHECK(igraph_neighbors(graph, &vneis,
                                              (igraph_integer_t) act, mode));
                n = (int) igraph_vector_size(&vneis);
                for (j = 0; j < n; j++) {
                    int nei = (int) VECTOR(vneis)[j];
                    if (VECTOR(counted)[nei] != mark) {
                        VECTOR(counted)[nei] = mark;
                        IGRAPH_CHECK(igraph_dqueue_long_push(&q, nei));
                        IGRAPH_CHECK(igraph_dqueue_long_push(&q, dist + 1));
                    }
                }
            }
        } /* while !igraph_dqueue_long_empty(dqueue) */

    } /* for IGRAPH_VIT_NEXT(vit) */

    if (!adjlist) {
        igraph_vector_destroy(&vneis);
        IGRAPH_FINALLY_CLEAN(1);
    }
    igraph_vector_int_destroy(&counted);
    igraph_vit_destroy(&vit);
    igraph_dqueue_long_destroy(&q);
    IGRAPH_FINALLY_CLEAN(3);

    return 0;
}

/**
 * \function igraph_eccentricity
 * Eccentricity of some vertices
 *
 * The eccentricity of a vertex is calculated by measuring the shortest
 * distance from (or to) the vertex, to (or from) all vertices in the
 * graph, and taking the maximum.
 *
 * </para><para>
 * This implementation ignores vertex pairs that are in different
 * components. Isolated vertices have eccentricity zero.
 *
 * \param graph The input graph, it can be directed or undirected.
 * \param res Pointer to an initialized vector, the result is stored
 *    here.
 * \param vids The vertices for which the eccentricity is calculated.
 * \param mode What kind of paths to consider for the calculation:
 *    \c IGRAPH_OUT, paths that follow edge directions;
 *    \c IGRAPH_IN, paths that follow the opposite directions; and
 *    \c IGRAPH_ALL, paths that ignore edge directions. This argument
 *    is ignored for undirected graphs.
 * \return Error code.
 *
 * Time complexity: O(v*(|V|+|E|)), where |V| is the number of
 * vertices, |E| is the number of edges and v is the number of
 * vertices for which eccentricity is calculated.
 *
 * \sa \ref igraph_radius().
 *
 * \example examples/simple/igraph_eccentricity.c
 */

int igraph_eccentricity(const igraph_t *graph,
                        igraph_vector_t *res,
                        igraph_vs_t vids,
                        igraph_neimode_t mode) {

    return igraph_i_eccentricity(graph, res, vids, mode, /*adjlist=*/ 0);
}

/**
 * \function igraph_radius
 * Radius of a graph
 *
 * The radius of a graph is the defined as the minimum eccentricity of
 * its vertices, see \ref igraph_eccentricity().
 *
 * \param graph The input graph, it can be directed or undirected.
 * \param radius Pointer to a real variable, the result is stored
 *   here.
 * \param mode What kind of paths to consider for the calculation:
 *    \c IGRAPH_OUT, paths that follow edge directions;
 *    \c IGRAPH_IN, paths that follow the opposite directions; and
 *    \c IGRAPH_ALL, paths that ignore edge directions. This argument
 *    is ignored for undirected graphs.
 * \return Error code.
 *
 * Time complexity: O(|V|(|V|+|E|)), where |V| is the number of
 * vertices and |E| is the number of edges.
 *
 * \sa \ref igraph_eccentricity().
 *
 * \example examples/simple/igraph_radius.c
 */

int igraph_radius(const igraph_t *graph, igraph_real_t *radius,
                  igraph_neimode_t mode) {

    int no_of_nodes = igraph_vcount(graph);

    if (no_of_nodes == 0) {
        *radius = IGRAPH_NAN;
    } else {
        igraph_adjlist_t adjlist;
        igraph_vector_t ecc;
        IGRAPH_CHECK(igraph_adjlist_init(graph, &adjlist, mode));
        IGRAPH_FINALLY(igraph_adjlist_destroy, &adjlist);
        IGRAPH_VECTOR_INIT_FINALLY(&ecc, igraph_vcount(graph));
        IGRAPH_CHECK(igraph_i_eccentricity(graph, &ecc, igraph_vss_all(),
                                           mode, &adjlist));
        *radius = igraph_vector_min(&ecc);
        igraph_vector_destroy(&ecc);
        igraph_adjlist_destroy(&adjlist);
        IGRAPH_FINALLY_CLEAN(2);
    }

    return 0;
}