I'm having some trouble with Floyd Warshall (all pairs shortest paths) in Boost graph. Is there any way to directly provide a directed weighted graph to floyd_warshall_all_pairs_shortest_paths? It seems like all its function overloadings require some extra parameters which I don't completely understand. Following is a test code I'm writing (it would not compile because my call to floyd_warshall_all_pairs_shortest_paths is incomplete)
#include <iostream>
#include <map>
#include <boost/graph/adjacency_list.hpp>
#include <boost/graph/floyd_warshall_shortest.hpp>
typedef boost::property<boost::edge_weight_t, double> EdgeWeightProperty;
typedef boost::adjacency_list<boost::vecS, boost::vecS,
boost::undirectedS, boost::no_property,
EdgeWeightProperty> Graph;
typedef unsigned long t_indx;
int main()
{
typedef boost::graph_traits<Graph>::vertex_descriptor vertex_des;
std::map<vertex_des, std::map<vertex_des, int> > matrix;
Graph sp_graph;
int edgelet_sp[] = { 1, 2,
1, 3,
1, 4,
2, 5,
3, 4,
3, 6,
4, 5,
4, 6,
4, 7,
5, 7,
6, 7 };
double edgelet_vals[] = { 4,
10,
3,
1,
12,
20,
6,
3,
0,
3,
9};
int num_edges = 11;
/* make the superpixel graph */
for (t_indx i = 0; i < num_edges; ++i) {
add_edge(edgelet_sp[i]-1, edgelet_sp[i+num_edges]-1, edgelet_vals[i], sp_graph);
}
std::cout << num_vertices(sp_graph) << std::endl;
bool floyd2 =
boost::floyd_warshall_all_pairs_shortest_paths
(sp_graph, matrix);
return 0;
}
I'm new to BGL so any help would be much appreciated. For instance, are there more elegant ways to write this code (sans the declaration of edgelet_sps and edgelet_vals, both of which will be replaced)? Thanks.
I figured (with the help of the inter-webs) that I need to use boost::get(boost::edge_weight, g) to directly supply an undirected weighted graph to floyd warshall. The following code compiles and works (here is a figure of the graph for the example below)
#include <iostream>
#include <boost/graph/undirected_graph.hpp>
#include <boost/graph/exterior_property.hpp>
#include <boost/graph/floyd_warshall_shortest.hpp>
// type for weight/distance on each edge
typedef double t_weight;
// define the graph type
typedef boost::property<boost::edge_weight_t, t_weight> EdgeWeightProperty;
typedef boost::adjacency_list<boost::vecS, boost::vecS, boost::undirectedS,
boost::no_property, EdgeWeightProperty> Graph;
typedef boost::property_map<Graph, boost::edge_weight_t>::type WeightMap;
// Declare a matrix type and its corresponding property map that
// will contain the distances between each pair of vertices.
typedef boost::exterior_vertex_property<Graph, t_weight> DistanceProperty;
typedef DistanceProperty::matrix_type DistanceMatrix;
typedef DistanceProperty::matrix_map_type DistanceMatrixMap;
int main()
{
Graph g;
const int num_edges = 11;
// define edges
int edges[] = { 1, 2,
1, 3,
1, 4,
2, 5,
3, 4,
3, 6,
4, 5,
4, 6,
4, 7,
5, 7,
6, 7 };
// define the weight on edges
t_weight weight[] = { 4,
10,
3,
1,
12,
20,
6,
3,
0,
3,
9 };
// iterate over all edges and insert them in the graph
for (std::size_t k = 0; k < num_edges; ++k)
boost::add_edge(edges[k*2]-1, edges[k*2+1]-1, weight[k], g);
WeightMap weight_pmap = boost::get(boost::edge_weight, g);
// set the distance matrix to receive the floyd warshall output
DistanceMatrix distances(num_vertices(g));
DistanceMatrixMap dm(distances, g);
// find all pairs shortest paths
bool valid = floyd_warshall_all_pairs_shortest_paths(g, dm,
boost::weight_map(weight_pmap));
// check if there no negative cycles
if (!valid) {
std::cerr << "Error - Negative cycle in matrix" << std::endl;
return -1;
}
// print upper triangular part of the distance matrix
std::cout << "Distance matrix: " << std::endl;
for (std::size_t i = 0; i < num_vertices(g); ++i) {
for (std::size_t j = i; j < num_vertices(g); ++j) {
std::cout << "From vertex " << i+1 << " to " << j+1 << " : ";
if(distances[i][j] == std::numeric_limits<t_weight>::max())
std::cout << "inf" << std::endl;
else
std::cout << distances[i][j] << std::endl;
}
std::cout << std::endl;
}
return 0;
}