1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/src/hugo/minlengthpaths.h Tue May 11 16:15:18 2004 +0000
1.3 @@ -0,0 +1,164 @@
1.4 +// -*- c++ -*-
1.5 +#ifndef HUGO_MINLENGTHPATHS_H
1.6 +#define HUGO_MINLENGTHPATHS_H
1.7 +
1.8 +///\ingroup galgs
1.9 +///\file
1.10 +///\brief An algorithm for finding k paths of minimal total length.
1.11 +
1.12 +#include <iostream>
1.13 +//#include <hugo/dijkstra.h>
1.14 +//#include <hugo/graph_wrapper.h>
1.15 +#include <hugo/maps.h>
1.16 +#include <vector>
1.17 +#include <hugo/mincostflows.h>
1.18 +#include <for_each_macros.h>
1.19 +
1.20 +namespace hugo {
1.21 +
1.22 +/// \addtogroup galgs
1.23 +/// @{
1.24 +
1.25 + ///\brief Implementation of an algorithm for finding k paths between 2 nodes
1.26 + /// of minimal total length
1.27 + ///
1.28 + /// The class \ref hugo::MinLengthPaths "MinLengthPaths" implements
1.29 + /// an algorithm for finding k edge-disjoint paths
1.30 + /// from a given source node to a given target node in an
1.31 + /// edge-weighted directed graph having minimal total weigth (length).
1.32 + ///
1.33 + ///\warning It is assumed that the lengths are positive, since the
1.34 + /// general flow-decomposition is not implemented yet.
1.35 + ///
1.36 + ///\author Attila Bernath
1.37 + template <typename Graph, typename LengthMap>
1.38 + class MinLengthPaths{
1.39 +
1.40 +
1.41 + typedef typename LengthMap::ValueType Length;
1.42 +
1.43 + typedef typename Graph::Node Node;
1.44 + typedef typename Graph::NodeIt NodeIt;
1.45 + typedef typename Graph::Edge Edge;
1.46 + typedef typename Graph::OutEdgeIt OutEdgeIt;
1.47 + typedef typename Graph::template EdgeMap<int> EdgeIntMap;
1.48 +
1.49 + typedef ConstMap<Edge,int> ConstMap;
1.50 +
1.51 + //Input
1.52 + const Graph& G;
1.53 +
1.54 + //Auxiliary variables
1.55 + //This is the capacity map for the mincostflow problem
1.56 + ConstMap const1map;
1.57 + //This MinCostFlows instance will actually solve the problem
1.58 + MinCostFlows<Graph, LengthMap, ConstMap> mincost_flow;
1.59 +
1.60 + //Container to store found paths
1.61 + std::vector< std::vector<Edge> > paths;
1.62 +
1.63 + public :
1.64 +
1.65 +
1.66 + MinLengthPaths(Graph& _G, LengthMap& _length) : G(_G),
1.67 + const1map(1), mincost_flow(_G, _length, const1map){}
1.68 +
1.69 + ///Runs the algorithm.
1.70 +
1.71 + ///Runs the algorithm.
1.72 + ///Returns k if there are at least k edge-disjoint paths from s to t.
1.73 + ///Otherwise it returns the number of found edge-disjoint paths from s to t.
1.74 + int run(Node s, Node t, int k) {
1.75 +
1.76 + int i = mincost_flow.run(s,t,k);
1.77 +
1.78 +
1.79 +
1.80 + //Let's find the paths
1.81 + //We put the paths into stl vectors (as an inner representation).
1.82 + //In the meantime we lose the information stored in 'reversed'.
1.83 + //We suppose the lengths to be positive now.
1.84 +
1.85 + //We don't want to change the flow of mincost_flow, so we make a copy
1.86 + //The name here suggests that the flow has only 0/1 values.
1.87 + EdgeIntMap reversed(G);
1.88 +
1.89 + FOR_EACH_LOC(typename Graph::EdgeIt, e, G){
1.90 + reversed[e] = mincost_flow.getFlow()[e];
1.91 + }
1.92 +
1.93 + paths.clear();
1.94 + //total_length=0;
1.95 + paths.resize(k);
1.96 + for (int j=0; j<i; ++j){
1.97 + Node n=s;
1.98 + OutEdgeIt e;
1.99 +
1.100 + while (n!=t){
1.101 +
1.102 +
1.103 + G.first(e,n);
1.104 +
1.105 + while (!reversed[e]){
1.106 + G.next(e);
1.107 + }
1.108 + n = G.head(e);
1.109 + paths[j].push_back(e);
1.110 + //total_length += length[e];
1.111 + reversed[e] = 1-reversed[e];
1.112 + }
1.113 +
1.114 + }
1.115 + return i;
1.116 + }
1.117 +
1.118 +
1.119 + ///This function gives back the total length of the found paths.
1.120 + ///Assumes that \c run() has been run and nothing changed since then.
1.121 + Length totalLength(){
1.122 + return mincost_flow.totalLength();
1.123 + }
1.124 +
1.125 + ///Returns a const reference to the EdgeMap \c flow. \pre \ref run() must
1.126 + ///be called before using this function.
1.127 + const EdgeIntMap &getFlow() const { return mincost_flow.flow;}
1.128 +
1.129 + ///Returns a const reference to the NodeMap \c potential (the dual solution).
1.130 + /// \pre \ref run() must be called before using this function.
1.131 + const EdgeIntMap &getPotential() const { return mincost_flow.potential;}
1.132 +
1.133 + ///This function checks, whether the given solution is optimal
1.134 + ///Running after a \c run() should return with true
1.135 + ///In this "state of the art" this only checks optimality, doesn't bother with feasibility
1.136 + ///
1.137 + ///\todo Is this OK here?
1.138 + bool checkComplementarySlackness(){
1.139 + return mincost_flow.checkComplementarySlackness();
1.140 + }
1.141 +
1.142 + ///This function gives back the \c j-th path in argument p.
1.143 + ///Assumes that \c run() has been run and nothing changed since then.
1.144 + /// \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).
1.145 + template<typename DirPath>
1.146 + void getPath(DirPath& p, size_t j){
1.147 +
1.148 + p.clear();
1.149 + if (j>paths.size()-1){
1.150 + return;
1.151 + }
1.152 + typename DirPath::Builder B(p);
1.153 + for(typename std::vector<Edge>::iterator i=paths[j].begin();
1.154 + i!=paths[j].end(); ++i ){
1.155 + B.pushBack(*i);
1.156 + }
1.157 +
1.158 + B.commit();
1.159 + }
1.160 +
1.161 + }; //class MinLengthPaths
1.162 +
1.163 + ///@}
1.164 +
1.165 +} //namespace hugo
1.166 +
1.167 +#endif //HUGO_MINLENGTHPATHS_H