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/* -*- mode: C -*- */
/*
IGraph library.
Copyright (C) 2006-2013 Gabor Csardi <csardi.gabor@gmail.com>
334 Harvard st, 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.h>
int validate_tree(const igraph_t *graph, const igraph_t *tree,
const igraph_vector_t *flow, const igraph_vector_t *capacity) {
igraph_integer_t n = igraph_vcount(graph);
igraph_vector_t edges;
igraph_real_t min_weight, flow_value;
long int i, j, k, m;
if (igraph_vcount(tree) != n) {
printf("Gomory-Hu tree should have %ld vertices\n", (long int)n);
return IGRAPH_EINVAL;
}
if (igraph_ecount(tree) != n-1) {
printf("Gomory-Hu tree should have %ld edges\n", (long int)n-1);
return IGRAPH_EINVAL;
}
if (igraph_is_directed(tree)) {
printf("Gomory-Hu tree should be undirected\n");
return IGRAPH_EINVAL;
}
if (n < 2)
return IGRAPH_SUCCESS;
IGRAPH_VECTOR_INIT_FINALLY(&edges, 0);
for (i = 0; i < n; i++) {
for (j = i+1; j < n; j++) {
IGRAPH_CHECK(igraph_get_shortest_path(tree, 0, &edges, i, j, IGRAPH_ALL));
m = igraph_vector_size(&edges);
if (m == 0)
continue;
min_weight = VECTOR(*flow)[(long int)VECTOR(edges)[0]];
for (k = 1; k < m; k++) {
if (VECTOR(*flow)[(long int)VECTOR(edges)[k]] < min_weight) {
min_weight = VECTOR(*flow)[(long int)VECTOR(edges)[k]];
}
}
IGRAPH_CHECK(igraph_maxflow(graph, &flow_value, 0, 0, 0, 0, i, j, capacity, 0));
if (flow_value != min_weight) {
printf("Min weight of path %ld --> %ld in Gomory-Hu tree is %.4f, "
"expected %.4f from flow calculation\n", i, j, min_weight, flow_value);
return IGRAPH_EINVAL;
}
}
}
igraph_vector_destroy(&edges);
IGRAPH_FINALLY_CLEAN(1);
return IGRAPH_SUCCESS;
}
int main() {
igraph_t g;
igraph_t tree;
igraph_vector_t flow;
igraph_vector_t capacity;
/* initialize flow and capacity vectors */
igraph_vector_init(&capacity, 0);
igraph_vector_init(&flow, 0);
/* empty undirected graph */
igraph_empty(&g, 0, 0);
if (igraph_gomory_hu_tree(&g, &tree, &flow, &capacity)) {
return 1;
}
if (igraph_vcount(&tree) != 0) {
return 1;
}
if (igraph_vector_size(&flow) != 0) {
return 1;
}
igraph_destroy(&tree);
igraph_destroy(&g);
/* simple undirected graph */
igraph_small(&g, 6, 0, 0, 1, 0, 2, 1, 2, 1, 3, 1, 4, 2, 4, 3, 4, 3, 5, 4, 5, -1);
igraph_vector_resize(&capacity, 9);
VECTOR(capacity)[0] = 1; VECTOR(capacity)[1] = 7; VECTOR(capacity)[2] = 1;
VECTOR(capacity)[3] = 3; VECTOR(capacity)[4] = 2; VECTOR(capacity)[5] = 4;
VECTOR(capacity)[6] = 1; VECTOR(capacity)[7] = 6; VECTOR(capacity)[8] = 2;
if (igraph_gomory_hu_tree(&g, &tree, &flow, &capacity)) {
return 2;
}
if (validate_tree(&g, &tree, &flow, &capacity)) {
return 2;
}
igraph_destroy(&tree);
/* Make sure we don't blow up without an outgoing flow vector */
if (igraph_gomory_hu_tree(&g, &tree, 0, &capacity)) {
return 2;
}
igraph_destroy(&tree);
igraph_destroy(&g);
/* simple directed graph - should throw an error */
igraph_small(&g, 6, 1, 0, 1, 0, 2, 1, 2, 1, 3, 1, 4, 2, 4, 3, 4, 3, 5, 4, 5, -1);
igraph_set_error_handler(igraph_error_handler_ignore);
if (!igraph_gomory_hu_tree(&g, &tree, &flow, &capacity)) {
return 3;
}
igraph_set_error_handler(igraph_error_handler_abort);
igraph_destroy(&g);
/* destroy flow and capacity vectors */
igraph_vector_destroy(&flow);
igraph_vector_destroy(&capacity);
return 0;
}
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