Igraph calculating minimum spanning tree with weights C interface

Question

I have been trying to calculate a minimum spanning tree using the prim method, but I have got rather confused about the way that weights are used in this context. The suggested example program in the source documents does not appear to be correct, I don't understand why the edge betweenness needs to be calculated. Please see the following program, it's 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);

    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;
}

Can anybody see anything that is wrong with this program it's designed to build a simple graph with what I hope is the correct way to use a weight argument. One value per edge between a source and a target.

Answer 1

The section about adding an edge betweenness comes from the original code example for the use of prim. It just needs to be removed for the program to work correctly using a user supply value of weight.