COIN-OR::LEMON - Graph Library

source: lemon-0.x/src/lemon/suurballe.h @ 933:1b7c88fbb950

Last change on this file since 933:1b7c88fbb950 was 921:818510fa3d99, checked in by Alpar Juttner, 16 years ago

hugo -> lemon

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1/* -*- C++ -*-
2 * src/lemon/suurballe.h - Part of LEMON, a generic C++ optimization library
3 *
4 * Copyright (C) 2004 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
5 * (Egervary Combinatorial Optimization Research Group, EGRES).
6 *
7 * Permission to use, modify and distribute this software is granted
8 * provided that this copyright notice appears in all copies. For
9 * precise terms see the accompanying LICENSE file.
10 *
11 * This software is provided "AS IS" with no warranty of any kind,
12 * express or implied, and with no claim as to its suitability for any
13 * purpose.
14 *
15 */
16
17#ifndef LEMON_SUURBALLE_H
18#define LEMON_SUURBALLE_H
19
20///\ingroup flowalgs
21///\file
22///\brief An algorithm for finding k paths of minimal total length.
23
24
25#include <lemon/maps.h>
26#include <vector>
27#include <lemon/min_cost_flow.h>
28
29namespace lemon {
30
31/// \addtogroup flowalgs
32/// @{
33
34  ///\brief Implementation of an algorithm for finding k edge-disjoint paths between 2 nodes
35  /// of minimal total length
36  ///
37  /// The class \ref lemon::Suurballe implements
38  /// an algorithm for finding k edge-disjoint paths
39  /// from a given source node to a given target node in an
40  /// edge-weighted directed graph having minimal total weight (length).
41  ///
42  ///\warning Length values should be nonnegative.
43  ///
44  ///\param Graph The directed graph type the algorithm runs on.
45  ///\param LengthMap The type of the length map (values should be nonnegative).
46  ///
47  ///\note It it questionable if it is correct to call this method after
48  ///%Suurballe for it is just a special case of Edmond's and Karp's algorithm
49  ///for finding minimum cost flows. In fact, this implementation is just
50  ///wraps the MinCostFlow algorithms. The paper of both %Suurballe and
51  ///Edmonds-Karp published in 1972, therefore it is possibly right to
52  ///state that they are
53  ///independent results. Most frequently this special case is referred as
54  ///%Suurballe method in the literature, especially in communication
55  ///network context.
56  ///\author Attila Bernath
57  template <typename Graph, typename LengthMap>
58  class Suurballe{
59
60
61    typedef typename LengthMap::ValueType Length;
62   
63    typedef typename Graph::Node Node;
64    typedef typename Graph::NodeIt NodeIt;
65    typedef typename Graph::Edge Edge;
66    typedef typename Graph::OutEdgeIt OutEdgeIt;
67    typedef typename Graph::template EdgeMap<int> EdgeIntMap;
68
69    typedef ConstMap<Edge,int> ConstMap;
70
71    //Input
72    const Graph& G;
73
74    //Auxiliary variables
75    //This is the capacity map for the mincostflow problem
76    ConstMap const1map;
77    //This MinCostFlow instance will actually solve the problem
78    MinCostFlow<Graph, LengthMap, ConstMap> mincost_flow;
79
80    //Container to store found paths
81    std::vector< std::vector<Edge> > paths;
82
83  public :
84
85
86    /// The constructor of the class.
87   
88    ///\param _G The directed graph the algorithm runs on.
89    ///\param _length The length (weight or cost) of the edges.
90    Suurballe(Graph& _G, LengthMap& _length) : G(_G),
91      const1map(1), mincost_flow(_G, _length, const1map){}
92
93    ///Runs the algorithm.
94
95    ///Runs the algorithm.
96    ///Returns k if there are at least k edge-disjoint paths from s to t.
97    ///Otherwise it returns the number of found edge-disjoint paths from s to t.
98    ///
99    ///\param s The source node.
100    ///\param t The target node.
101    ///\param k How many paths are we looking for?
102    ///
103    int run(Node s, Node t, int k) {
104
105      int i = mincost_flow.run(s,t,k);
106   
107
108      //Let's find the paths
109      //We put the paths into stl vectors (as an inner representation).
110      //In the meantime we lose the information stored in 'reversed'.
111      //We suppose the lengths to be positive now.
112
113      //We don't want to change the flow of mincost_flow, so we make a copy
114      //The name here suggests that the flow has only 0/1 values.
115      EdgeIntMap reversed(G);
116
117      for(typename Graph::EdgeIt e(G); e!=INVALID; ++e)
118        reversed[e] = mincost_flow.getFlow()[e];
119     
120      paths.clear();
121      //total_length=0;
122      paths.resize(k);
123      for (int j=0; j<i; ++j){
124        Node n=s;
125        OutEdgeIt e;
126
127        while (n!=t){
128
129
130          G.first(e,n);
131         
132          while (!reversed[e]){
133            ++e;
134          }
135          n = G.head(e);
136          paths[j].push_back(e);
137          //total_length += length[e];
138          reversed[e] = 1-reversed[e];
139        }
140       
141      }
142      return i;
143    }
144
145   
146    ///Returns the total length of the paths
147   
148    ///This function gives back the total length of the found paths.
149    ///\pre \ref run() must
150    ///be called before using this function.
151    Length totalLength(){
152      return mincost_flow.totalLength();
153    }
154
155    ///Returns the found flow.
156
157    ///This function returns a const reference to the EdgeMap \c flow.
158    ///\pre \ref run() must
159    ///be called before using this function.
160    const EdgeIntMap &getFlow() const { return mincost_flow.flow;}
161
162    /// Returns the optimal dual solution
163   
164    ///This function returns a const reference to the NodeMap
165    ///\c potential (the dual solution).
166    /// \pre \ref run() must be called before using this function.
167    const EdgeIntMap &getPotential() const { return mincost_flow.potential;}
168
169    ///Checks whether the complementary slackness holds.
170
171    ///This function checks, whether the given solution is optimal.
172    ///It should return true after calling \ref run()
173    ///Currently this function only checks optimality,
174    ///doesn't bother with feasibility
175    ///It is meant for testing purposes.
176    ///
177    bool checkComplementarySlackness(){
178      return mincost_flow.checkComplementarySlackness();
179    }
180
181    ///Read the found paths.
182   
183    ///This function gives back the \c j-th path in argument p.
184    ///Assumes that \c run() has been run and nothing changed since then.
185    /// \warning It is assumed that \c p is constructed to
186    ///be a path of graph \c G.
187    ///If \c j is not less than the result of previous \c run,
188    ///then the result here will be an empty path (\c j can be 0 as well).
189    ///
190    ///\param Path The type of the path structure to put the result to (must meet lemon path concept).
191    ///\param p The path to put the result to
192    ///\param j Which path you want to get from the found paths (in a real application you would get the found paths iteratively)
193    template<typename Path>
194    void getPath(Path& p, size_t j){
195
196      p.clear();
197      if (j>paths.size()-1){
198        return;
199      }
200      typename Path::Builder B(p);
201      for(typename std::vector<Edge>::iterator i=paths[j].begin();
202          i!=paths[j].end(); ++i ){
203        B.pushBack(*i);
204      }
205
206      B.commit();
207    }
208
209  }; //class Suurballe
210
211  ///@}
212
213} //namespace lemon
214
215#endif //LEMON_SUURBALLE_H
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