EdgeMap and NodeMap creation is done, at last. Bach 4ever.
2 * demo/lp_maxflow_demo.cc - Part of LEMON, a generic C++ optimization library
4 * Copyright (C) 2005 Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
5 * (Egervary Research Group on Combinatorial Optimization, EGRES).
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.
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
19 ///\brief Max flow problem solved with an LP solver (demo).
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 LP
24 /// constraints that arise in graph theory in our library LEMON .
30 #include<lemon/graph_reader.h>
31 #include<lemon/list_graph.h>
38 #include <lemon/lp_glpk.h>
40 #include <lemon/lp_cplex.h>
43 using namespace lemon;
46 typedef LpGlpk LpDefault;
47 const char default_solver_name[]="GLPK";
49 typedef LpCplex LpDefault;
50 const char default_solver_name[]="CPLEX";
54 template<class G,class C>
55 double maxFlow(const G &g,const C &cap,typename G::Node s,typename G::Node t)
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;
67 //Define a map on the edges for the variables of the LP problem
68 typename G::template EdgeMap<LpDefault::Col> x(g);
71 //Nonnegativity and capacity constraints
72 for(EdgeIt e(g);e!=INVALID;++e) {
73 lp.colUpperBound(x[e],cap[e]);
74 lp.colLowerBound(x[e],0);
78 //Flow conservation constraints for the nodes (except for 's' and 't')
79 for(NodeIt n(g);n!=INVALID;++n) if(n!=s&&n!=t) {
81 for(InEdgeIt e(g,n);e!=INVALID;++e) ex+=x[e];
82 for(OutEdgeIt e(g,n);e!=INVALID;++e) ex-=x[e];
86 //Objective function: the flow value entering 't'
88 for(InEdgeIt e(g,t);e!=INVALID;++e) obj+=x[e];
89 for(OutEdgeIt e(g,t);e!=INVALID;++e) obj-=x[e];
101 std::cout<<"Solver used: "<<default_solver_name<<std::endl;
103 //Solve with the underlying solver
106 return lp.primalValue();
109 int main(int argc, char *argv[])
113 std::cerr << " USAGE: lp_maxflow_demo input_file.lgf" << std::endl;
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)."
122 //input stream to read the graph from
123 std::ifstream is(argv[1]);
130 ListGraph::EdgeMap<double> cap(g);
132 GraphReader<ListGraph> reader(is,g);
133 reader.readNode("source",s).readNode("target",t)
134 .readEdgeMap("capacity",cap).run();
136 std::cout << "Max flow value = " << maxFlow(g,cap,s,t) << std::endl;