COIN-OR::LEMON - Graph Library

source: lemon-0.x/demo/lp_maxflow_demo.cc @ 1577:15098fb5275c

Last change on this file since 1577:15098fb5275c was 1577:15098fb5275c, checked in by athos, 15 years ago

Documentation (lp_demo,lp_maxflow) and slight changes (rest).

File size: 3.4 KB
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[1560]1/* -*- C++ -*-
2 * demo/lp_maxflow_demo.cc - Part of LEMON, a generic C++ optimization library
3 *
4 * Copyright (C) 2005 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
5 * (Egervary Research Group on Combinatorial Optimization, 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///\ingroup demos
18///\file
19///\brief Max flow problem solved with an LP solver (demo).
20///
21///This demo program shows how to solve a maximum (or maximal) flow
22///problem using the LEMON LP solver interface. We would like to lay
23///the emphasis on the simplicity of the way one can formulate the LP
24///constraints with LEMON that arise in graph theory.
25
[1387]26#ifdef HAVE_CONFIG_H
27#include <config.h>
28#endif
29
[1361]30#include<lemon/graph_reader.h>
31#include<lemon/list_graph.h>
32
[1560]33#include <fstream>
34#include <iostream>
35
[1381]36
37#ifdef HAVE_GLPK
38#include <lemon/lp_glpk.h>
39#elif HAVE_CPLEX
40#include <lemon/lp_cplex.h>
41#endif
42
[1361]43using namespace lemon;
44
[1381]45#ifdef HAVE_GLPK
46typedef LpGlpk LpDefault;
[1577]47const char default_solver_name[]="GLPK";
[1381]48#elif HAVE_CPLEX
49typedef LpCplex LpDefault;
[1577]50const char default_solver_name[]="CPLEX";
[1381]51#endif
52
53
[1361]54template<class G,class C>
55double maxFlow(const G &g,const C &cap,typename G::Node s,typename G::Node t)
56{
[1381]57  LpDefault lp;
[1361]58 
59  typedef G Graph;
60  typedef typename G::Node Node;
61  typedef typename G::NodeIt NodeIt;
62  typedef typename G::Edge Edge;
63  typedef typename G::EdgeIt EdgeIt;
64  typedef typename G::OutEdgeIt OutEdgeIt;
65  typedef typename G::InEdgeIt InEdgeIt;
66 
[1518]67  //Define a map on the edges for the variables of the LP problem
[1381]68  typename G::template EdgeMap<LpDefault::Col> x(g);
[1361]69  lp.addColSet(x);
70 
[1518]71  //Nonnegativity and capacity constraints
[1361]72  for(EdgeIt e(g);e!=INVALID;++e) {
73    lp.colUpperBound(x[e],cap[e]);
74    lp.colLowerBound(x[e],0);
75  }
76
[1518]77
78  //Flow conservation constraints for the nodes (except for 's' and 't')
[1361]79  for(NodeIt n(g);n!=INVALID;++n) if(n!=s&&n!=t) {
[1381]80    LpDefault::Expr ex;
[1361]81    for(InEdgeIt  e(g,n);e!=INVALID;++e) ex+=x[e];
82    for(OutEdgeIt e(g,n);e!=INVALID;++e) ex-=x[e];
83    lp.addRow(ex==0);
84  }
[1518]85 
86  //Objective function: the flow value entering 't'
[1571]87  LpDefault::Expr obj;
88  for(InEdgeIt  e(g,t);e!=INVALID;++e) obj+=x[e];
89  for(OutEdgeIt e(g,t);e!=INVALID;++e) obj-=x[e];
90  lp.setObj(obj);
91
[1518]92
93  //Maximization
[1361]94  lp.max();
95
[1381]96#ifdef HAVE_GLPK
[1361]97  lp.presolver(true);
98  lp.messageLevel(3);
[1381]99#endif
[1361]100
[1577]101  std::cout<<"Solver used: "<<default_solver_name<<std::endl;
102
[1518]103  //Solve with the underlying solver
[1361]104  lp.solve();
105
106  return lp.primalValue();
107}
108
[1560]109int main(int argc, char *argv[])
[1361]110{
[1560]111  if(argc<2)
112  {
[1577]113      std::cerr << "  USAGE: lp_maxflow_demo input_file.lgf" << std::endl;
[1561]114      std::cerr << "  The file 'input_file.lgf' has to contain a max "
115                << "flow instance in\n"
116                << "  LEMON format (e.g. sample.lgf is such a file)."
117                << std::endl;
[1560]118      return 0;
119  }
120
121
122  //input stream to read the graph from
123  std::ifstream is(argv[1]);
124
125
[1361]126  ListGraph g;
127  ListGraph::Node s;
128  ListGraph::Node t;
129 
130  ListGraph::EdgeMap<double> cap(g);
131 
[1560]132  GraphReader<ListGraph> reader(is,g);
[1394]133  reader.readNode("source",s).readNode("target",t)
134    .readEdgeMap("capacity",cap).run();
[1361]135 
136  std::cout << "Max flow value = " << maxFlow(g,cap,s,t) << std::endl;
137
138}
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