Finished MinLengthPaths: a specialization of MinCostFlows.
2 #ifndef HUGO_MINLENGTHPATHS_H
3 #define HUGO_MINLENGTHPATHS_H
7 ///\brief An algorithm for finding k paths of minimal total length.
10 //#include <hugo/dijkstra.h>
11 //#include <hugo/graph_wrapper.h>
12 #include <hugo/maps.h>
14 #include <mincostflows.h>
15 #include <for_each_macros.h>
22 ///\brief Implementation of an algorithm for finding k paths between 2 nodes
23 /// of minimal total length
25 /// The class \ref hugo::MinLengthPaths "MinLengthPaths" implements
26 /// an algorithm for finding k edge-disjoint paths
27 /// from a given source node to a given target node in an
28 /// edge-weighted directed graph having minimal total weigth (length).
30 ///\warning It is assumed that the lengths are positive, since the
31 /// general flow-decomposition is not implemented yet.
33 ///\author Attila Bernath
34 template <typename Graph, typename LengthMap>
38 typedef typename LengthMap::ValueType Length;
40 typedef typename Graph::Node Node;
41 typedef typename Graph::NodeIt NodeIt;
42 typedef typename Graph::Edge Edge;
43 typedef typename Graph::OutEdgeIt OutEdgeIt;
44 typedef typename Graph::template EdgeMap<int> EdgeIntMap;
46 typedef ConstMap<Edge,int> ConstMap;
52 //This is the capacity map for the mincostflow problem
54 //This MinCostFlows instance will actually solve the problem
55 MinCostFlows<Graph, LengthMap, ConstMap> mincost_flow;
57 //Container to store found paths
58 std::vector< std::vector<Edge> > paths;
63 MinLengthPaths(Graph& _G, LengthMap& _length) : G(_G),
64 const1map(1), mincost_flow(_G, _length, const1map){}
66 ///Runs the algorithm.
68 ///Runs the algorithm.
69 ///Returns k if there are at least k edge-disjoint paths from s to t.
70 ///Otherwise it returns the number of found edge-disjoint paths from s to t.
71 int run(Node s, Node t, int k) {
73 int i = mincost_flow.run(s,t,k);
77 //Let's find the paths
78 //We put the paths into stl vectors (as an inner representation).
79 //In the meantime we lose the information stored in 'reversed'.
80 //We suppose the lengths to be positive now.
82 //We don't want to change the flow of mincost_flow, so we make a copy
83 //The name here suggests that the flow has only 0/1 values.
84 EdgeIntMap reversed(G);
86 FOR_EACH_LOC(typename Graph::EdgeIt, e, G){
87 reversed[e] = mincost_flow.getFlow()[e];
93 for (int j=0; j<i; ++j){
102 while (!reversed[e]){
106 paths[j].push_back(e);
107 //total_length += length[e];
108 reversed[e] = 1-reversed[e];
116 ///This function gives back the total length of the found paths.
117 ///Assumes that \c run() has been run and nothing changed since then.
118 Length totalLength(){
119 return mincost_flow.totalLength();
122 ///Returns a const reference to the EdgeMap \c flow. \pre \ref run() must
123 ///be called before using this function.
124 const EdgeIntMap &getFlow() const { return mincost_flow.flow;}
126 ///Returns a const reference to the NodeMap \c potential (the dual solution).
127 /// \pre \ref run() must be called before using this function.
128 const EdgeIntMap &getPotential() const { return mincost_flow.potential;}
130 ///This function checks, whether the given solution is optimal
131 ///Running after a \c run() should return with true
132 ///In this "state of the art" this only checks optimality, doesn't bother with feasibility
134 ///\todo Is this OK here?
135 bool checkComplementarySlackness(){
136 return mincost_flow.checkComplementarySlackness();
139 ///This function gives back the \c j-th path in argument p.
140 ///Assumes that \c run() has been run and nothing changed since then.
141 /// \warning It is assumed that \c p is constructed to be a path of graph \c G. If \c j is not less than the result of previous \c run, then the result here will be an empty path (\c j can be 0 as well).
142 template<typename DirPath>
143 void getPath(DirPath& p, size_t j){
146 if (j>paths.size()-1){
149 typename DirPath::Builder B(p);
150 for(typename std::vector<Edge>::iterator i=paths[j].begin();
151 i!=paths[j].end(); ++i ){
158 }; //class MinLengthPaths
164 #endif //HUGO_MINLENGTHPATHS_H