
From:  Szabolcs Horvát 
Subject:  Re: [igraph] Igraph calculating minimum spanning tree with weights C interface 
Date:  Tue, 29 Mar 2016 16:53:57 +0200 
I have been trying to calculate a minimum spanning tree using prim method, but I have got a little bit confused about the weights are used in this context. The suggest example program in the source documents does not seem to be correct, I don't understand why the edge betweenness needs to be calculated.
Please see the following program, its designed to make a simple undirected graph.
#include <igraph.h> int main() { igraph_vector_t eb, edges; igraph_vector_t weights; long int i; igraph_t theGraph, tree; struct arg { int index; int source; int target; float weight; }; struct arg data[] = { {0, 0, 1, 2.0}, {1, 1, 2, 3.0}, {2, 2, 3, 44.0}, {3, 3, 4, 3.0}, {4, 4, 1, 2.0}, {5, 4, 5, 9.0}, {6, 4, 6, 3.0}, {6, 6, 5, 7.0} }; int nargs = sizeof(data) / sizeof(struct arg); igraph_empty(&theGraph, nargs, IGRAPH_UNDIRECTED);
Can anybody see anything that is wrong with this program its designed to build a simple graph with what I hope is the correct way to use a weight argument.igraph_vector_init(&weights, nargs); // create graph for (i = 0; i < nargs; i++) { igraph_add_edge(&theGraph, data[i].source, data[i].target); // Add an weight per entry igraph_vector_set(&weights, i, data[i].weight); } igraph_vector_init(&eb, igraph_ecount(&theGraph)); igraph_edge_betweenness(&theGraph, &eb, IGRAPH_UNDIRECTED, &weights); for (i = 0; i < igraph_vector_size(&eb); i++) { VECTOR(eb)[i] = VECTOR(eb)[i]; } igraph_minimum_spanning_tree_prim(&theGraph, &tree, &eb); igraph_write_graph_edgelist(&tree, stdout); igraph_vector_init(&edges, 0); igraph_minimum_spanning_tree(&theGraph, &edges, &eb); igraph_vector_print(&edges); igraph_vector_destroy(&edges); igraph_destroy(&tree); igraph_destroy(&theGraph); igraph_vector_destroy(&eb); return 0; }
One value per edge between a source and a target.
regards
Dave.
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