Reformatting: too long code lines.
2 * demo/lp_maxflow_demo.cc - Part of LEMON, a generic C++ optimization library
4 * Copyright (C) 2006 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 .
26 /// \include lp_maxflow_demo.cc
28 #include<lemon/graph_reader.h>
29 #include<lemon/list_graph.h>
37 using namespace lemon;
39 template<class G,class C>
40 double maxFlow(const G &g,const C &cap,typename G::Node s,typename G::Node t)
45 typedef typename G::Node Node;
46 typedef typename G::NodeIt NodeIt;
47 typedef typename G::Edge Edge;
48 typedef typename G::EdgeIt EdgeIt;
49 typedef typename G::OutEdgeIt OutEdgeIt;
50 typedef typename G::InEdgeIt InEdgeIt;
52 //Define a map on the edges for the variables of the LP problem
53 typename G::template EdgeMap<Lp::Col> x(g);
56 //Nonnegativity and capacity constraints
57 for(EdgeIt e(g);e!=INVALID;++e) {
58 lp.colUpperBound(x[e],cap[e]);
59 lp.colLowerBound(x[e],0);
63 //Flow conservation constraints for the nodes (except for 's' and 't')
64 for(NodeIt n(g);n!=INVALID;++n) if(n!=s&&n!=t) {
66 for(InEdgeIt e(g,n);e!=INVALID;++e) ex+=x[e];
67 for(OutEdgeIt e(g,n);e!=INVALID;++e) ex-=x[e];
71 //Objective function: the flow value entering 't'
73 for(InEdgeIt e(g,t);e!=INVALID;++e) obj+=x[e];
74 for(OutEdgeIt e(g,t);e!=INVALID;++e) obj-=x[e];
86 std::cout<<"Solver used: "<<default_solver_name<<std::endl;
88 //Solve with the underlying solver
91 return lp.primalValue();
94 int main(int argc, char *argv[])
98 std::cerr << " USAGE: lp_maxflow_demo input_file.lgf" << std::endl;
99 std::cerr << " The file 'input_file.lgf' has to contain a max "
100 << "flow instance in\n"
101 << " LEMON format (e.g. sample.lgf is such a file)."
107 //input stream to read the graph from
108 std::ifstream is(argv[1]);
115 ListGraph::EdgeMap<double> cap(g);
117 GraphReader<ListGraph> reader(is,g);
118 reader.readNode("source",s).readNode("target",t)
119 .readEdgeMap("capacity",cap).run();
121 std::cout << "Max flow value = " << maxFlow(g,cap,s,t) << std::endl;