Thank you for your replies. 2010/2/7 Andrew Sutton <andrew.n.sutton@gmail.com>
std::pair< graph_traits<Graph>::edge_descriptor, bool > p = add_edge (*vertices(g).first, *vertices(g).second, g);
The function vertices returns an iterator range. In my understanding an iterator range is a pair of iterators [first, second) so that second can be reached from first with increment operations, _but_ is not part of the iterator range itself. It could be an iterator like one returned by the end-function of a stl-vector. It shall not be dereferenced!
I'll also add that adjacency_list with vecS as a vertex set will add vertices in add_edge if an invalid vertex descriptor is given -- of which vertices(g).second is an invalid itetator. It's equivalent to end(vertices(g)) if you're using Boost.Range.
I understand. Obviously, dereferencing a past the end iterator is a bad idea. I am now facing another problem using kolmogorov_max_flow algorithm. Here is the code: #include <iostream> #include <vector> using namespace std; #include <boost/graph/kolmogorov_max_flow.hpp> #include <boost/graph/adjacency_list.hpp> using namespace boost; typedef adjacency_list_traits < vecS, vecS, directedS > Traits; typedef adjacency_list < vecS, vecS, directedS, property < vertex_index_t, long, property < vertex_color_t, boost::default_color_type, property < vertex_distance_t, long, property < vertex_potential_t, long, // stores the unary energy associated to each vertex property < vertex_predecessor_t, Traits::edge_descriptor > > > > >, property < edge_capacity_t, long, // stores the binary energy associated to each edge property < edge_residual_capacity_t, long, property < edge_reverse_t, Traits::edge_descriptor > > > > Graph; int main(int argc, char** argv) { Graph g; property_map<Graph, edge_capacity_t>::type capacity = get(edge_capacity, g); property_map<Graph, edge_reverse_t>::type rev = get(edge_reverse, g); graph_traits<Graph>::vertex_iterator v_first, v_second, v_third; v_first = vertices(g).first; v_second = v_first; ++v_second; v_third = v_second; ++v_third; std::pair< graph_traits<Graph>::edge_descriptor, bool > p = add_edge(*v_first, *v_second, g); capacity[p.first] = 10; std::pair< graph_traits<Graph>::edge_descriptor, bool > p_reverse = add_edge(*v_second, *v_first, g); rev[p.first] = p_reverse.first; capacity[p_reverse.first] = -10; std::pair< graph_traits<Graph>::edge_descriptor, bool > p2 = add_edge(*v_second, *v_third, g); capacity[p2.first] = 11; std::pair< graph_traits<Graph>::edge_descriptor, bool > p2_reverse = add_edge(*v_third, *v_second, g); rev[p2.first] = p2_reverse.first; capacity[p2_reverse.first] = -11; std::cout << "num_vertices = " << num_vertices(g) << std::endl; std::cout << "num_edges = " << num_edges(g) << std::endl; long flow = kolmogorov_max_flow(g , *v_first, *v_third); std::cout << "flow = " << flow << std::endl; return 0; } The code below crashes (segfault) in the max_flow() function. Could you tell me what am I doing wrong ? It seems to work when I set a capacity capacity[p2.first] with a value smaller than 10 (capacity[p.first]). Am I missing something? Do I correctly use the reverse property_map? Hope you could help. Regards, Olivier
Andrew Sutton andrew.n.sutton@gmail.com
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