1 //=======================================================================
2 // Copyright 2001 Jeremy G. Siek, Andrew Lumsdaine, Lie-Quan Lee,
3 //
4 // Distributed under the Boost Software License, Version 1.0. (See
5 // accompanying file LICENSE_1_0.txt or copy at
6 // http://www.boost.org/LICENSE_1_0.txt)
7 //=======================================================================
8 #include <boost/config.hpp>
9 #include <vector>
10 #include <iostream>
11 #include <fstream>
12 #include <iomanip>
13 #include <boost/graph/adjacency_list.hpp>
14 #include <boost/graph/bellman_ford_shortest_paths.hpp>
15
16 using namespace boost;
17
18 template < typename Graph, typename ParentMap >
19 struct edge_writer
20 {
edge_writeredge_writer21 edge_writer(const Graph & g, const ParentMap & p)
22 : m_g(g), m_parent(p)
23 {
24 }
25
26 template < typename Edge >
operator ()edge_writer27 void operator() (std::ostream & out, const Edge & e) const
28 {
29 out << "[label=\"" << get(edge_weight, m_g, e) << "\"";
30 typename graph_traits < Graph >::vertex_descriptor
31 u = source(e, m_g), v = target(e, m_g);
32 if (m_parent[v] == u)
33 out << ", color=\"black\"";
34 else
35 out << ", color=\"grey\"";
36 out << "]";
37 }
38 const Graph & m_g;
39 ParentMap m_parent;
40 };
41 template < typename Graph, typename Parent >
42 edge_writer < Graph, Parent >
make_edge_writer(const Graph & g,const Parent & p)43 make_edge_writer(const Graph & g, const Parent & p)
44 {
45 return edge_writer < Graph, Parent > (g, p);
46 }
47
48 struct EdgeProperties {
49 int weight;
50 };
51
52 int
main()53 main()
54 {
55 enum { u, v, x, y, z, N };
56 char name[] = { 'u', 'v', 'x', 'y', 'z' };
57 typedef std::pair < int, int >E;
58 const int n_edges = 10;
59 E edge_array[] = { E(u, y), E(u, x), E(u, v), E(v, u),
60 E(x, y), E(x, v), E(y, v), E(y, z), E(z, u), E(z,x) };
61 int weight[n_edges] = { -4, 8, 5, -2, 9, -3, 7, 2, 6, 7 };
62
63 typedef adjacency_list < vecS, vecS, directedS,
64 no_property, EdgeProperties> Graph;
65 #if defined(BOOST_MSVC) && BOOST_MSVC <= 1300
66 // VC++ can't handle the iterator constructor
67 Graph g(N);
68 for (std::size_t j = 0; j < n_edges; ++j)
69 add_edge(edge_array[j].first, edge_array[j].second, g);
70 #else
71 Graph g(edge_array, edge_array + n_edges, N);
72 #endif
73 graph_traits < Graph >::edge_iterator ei, ei_end;
74 property_map<Graph, int EdgeProperties::*>::type
75 weight_pmap = get(&EdgeProperties::weight, g);
76 int i = 0;
77 for (boost::tie(ei, ei_end) = edges(g); ei != ei_end; ++ei, ++i)
78 weight_pmap[*ei] = weight[i];
79
80 std::vector<int> distance(N, (std::numeric_limits < short >::max)());
81 std::vector<std::size_t> parent(N);
82 for (i = 0; i < N; ++i)
83 parent[i] = i;
84 distance[z] = 0;
85
86 #if defined(BOOST_MSVC) && BOOST_MSVC <= 1300
87 bool r = bellman_ford_shortest_paths
88 (g, int(N), weight_pmap, &parent[0], &distance[0],
89 closed_plus<int>(), std::less<int>(), default_bellman_visitor());
90 #else
91 bool r = bellman_ford_shortest_paths
92 (g, int (N), weight_map(weight_pmap).distance_map(&distance[0]).
93 predecessor_map(&parent[0]));
94 #endif
95
96 if (r)
97 for (i = 0; i < N; ++i)
98 std::cout << name[i] << ": " << std::setw(3) << distance[i]
99 << " " << name[parent[i]] << std::endl;
100 else
101 std::cout << "negative cycle" << std::endl;
102
103 std::ofstream dot_file("figs/bellman-eg.dot");
104 dot_file << "digraph D {\n"
105 << " rankdir=LR\n"
106 << " size=\"5,3\"\n"
107 << " ratio=\"fill\"\n"
108 << " edge[style=\"bold\"]\n" << " node[shape=\"circle\"]\n";
109
110 {
111 for (boost::tie(ei, ei_end) = edges(g); ei != ei_end; ++ei) {
112 graph_traits < Graph >::edge_descriptor e = *ei;
113 graph_traits < Graph >::vertex_descriptor
114 u = source(e, g), v = target(e, g);
115 // VC++ doesn't like the 3-argument get function, so here
116 // we workaround by using 2-nested get()'s.
117 dot_file << name[u] << " -> " << name[v]
118 << "[label=\"" << get(get(&EdgeProperties::weight, g), e) << "\"";
119 if (parent[v] == u)
120 dot_file << ", color=\"black\"";
121 else
122 dot_file << ", color=\"grey\"";
123 dot_file << "]";
124 }
125 }
126 dot_file << "}";
127 return EXIT_SUCCESS;
128 }
129