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/*
igraph library.
Copyright (C) 2006-2024 The igraph development team <igraph@igraph.org>
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, see <https://www.gnu.org/licenses/>.
*/
#include <igraph.h>
int main(void) {
igraph_t graph;
igraph_vector_t eb;
igraph_vector_int_t edges;
/* Initialize the library. */
igraph_setup();
/* Create the vector where the tree edges will be stored. */
igraph_vector_int_init(&edges, 0);
/* Create the Frucht graph */
igraph_famous(&graph, "Frucht");
/* Compute the edge betweenness. */
igraph_vector_init(&eb, igraph_ecount(&graph));
igraph_edge_betweenness(&graph, /*weights=*/ NULL, &eb, igraph_ess_all(IGRAPH_EDGEORDER_ID), IGRAPH_UNDIRECTED, false);
/* Use Prim's algorithm to compute the edges that belong to the minimum weight
* spanning tree, using edge betweenness values as edge weights. */
igraph_minimum_spanning_tree(&graph, &edges, &eb, IGRAPH_MST_PRIM);
printf("Minimum spanning tree edges:\n");
igraph_vector_int_print(&edges);
/* A maximum spanning tree can be computed by first negating the weights. */
igraph_vector_scale(&eb, -1);
/* Compute and output the edges that belong to the maximum weight spanning tree,
* letting igraph automatically select the most suitable algorithm. */
igraph_minimum_spanning_tree(&graph, &edges, &eb, IGRAPH_MST_AUTOMATIC);
printf("\nMaximum spanning tree edges:\n");
igraph_vector_int_print(&edges);
igraph_real_t total_tree_weight = 0;
igraph_int_t n = igraph_vector_int_size(&edges);
for (igraph_int_t i=0; i < n; i++) {
total_tree_weight += -VECTOR(eb)[ VECTOR(edges)[i] ];
}
printf("\nTotal maximum spanning tree weight: %g\n", total_tree_weight);
/* Clean up */
igraph_destroy(&graph);
igraph_vector_destroy(&eb);
igraph_vector_int_destroy(&edges);
return 0;
}
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