COIN-OR::LEMON - Graph Library

source: lemon-0.x/src/demo/lp_demo.cc @ 1322:cfc26d103bcf

Last change on this file since 1322:cfc26d103bcf was 1322:cfc26d103bcf, checked in by Alpar Juttner, 15 years ago

Demo prog that computes the max flow by LP

File size: 1.5 KB
Line 
1#include<lemon/lp_glpk.h>
2#include<lemon/graph_reader.h>
3#include<lemon/list_graph.h>
4
5using namespace lemon;
6
7template<class G,class C>
8double maxFlow(const G &g,const C &cap,typename G::Node s,typename G::Node t)
9{
10  LpGlpk lp;
11 
12  typedef G Graph;
13  typedef typename G::Node Node;
14  typedef typename G::NodeIt NodeIt;
15  typedef typename G::Edge Edge;
16  typedef typename G::EdgeIt EdgeIt;
17  typedef typename G::OutEdgeIt OutEdgeIt;
18  typedef typename G::InEdgeIt InEdgeIt;
19 
20  typename G::template EdgeMap<LpGlpk::Col> x(g);
21  lp.addColSet(x);
22 
23  for(EdgeIt e(g);e!=INVALID;++e) {
24    lp.colUpperBound(x[e],cap[e]);
25    lp.colLowerBound(x[e],0);
26  }
27
28  for(NodeIt n(g);n!=INVALID;++n) if(n!=s&&n!=t) {
29    LpGlpk::Expr ex;
30    for(InEdgeIt  e(g,n);e!=INVALID;++e) ex+=x[e];
31    for(OutEdgeIt e(g,n);e!=INVALID;++e) ex-=x[e];
32    lp.addRow(ex==0);
33  }
34  {
35    LpGlpk::Expr ex;
36    for(InEdgeIt  e(g,t);e!=INVALID;++e) ex+=x[e];
37    for(OutEdgeIt e(g,t);e!=INVALID;++e) ex-=x[e];
38    lp.setObj(ex);
39  }
40  lp.max();
41  lp.solve();
42
43  return lp.primalValue();
44}
45
46int main()
47{
48  LpGlpk lp_glpk;
49
50  ListGraph g;
51  ListGraph::Node s;
52  ListGraph::Node t;
53 
54
55  ListGraph::EdgeMap<double> cap(g);
56 
57  GraphReader<ListGraph> reader(std::cin,g);
58  reader.addNode("source",s).addNode("target",t)
59    .addEdgeMap("capacity",cap).run();
60 
61  // std::ifstream file("../test/preflow_");
62//   readDimacs(file, g, cap, s, t);
63
64  std::cout << "Max flow value = " << maxFlow(g,cap,s,t) << std::endl;
65
66}
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