source: lemon-0.x/src/work/marci/lp/max_flow_expression.cc @ 1143:4fb22cfa5759

// -*- c++ -*-
#include <iostream>
#include <fstream>

#include <lemon/graph_utils.h>
#include <lemon/smart_graph.h>
#include <lemon/list_graph.h>
#include <lemon/dimacs.h>
#include <lemon/time_measure.h>
#include <lp_solver_base.h>

using std::cout;
using std::endl;
using namespace lemon;

template<typename Edge, typename EdgeIndexMap> 
class PrimalMap {
protected:
  LPGLPK* lp;
  EdgeIndexMap* edge_index_map;
public:
  PrimalMap(LPGLPK& _lp, EdgeIndexMap& _edge_index_map) : 
    lp(&_lp), edge_index_map(&_edge_index_map) { }
  double operator[](Edge e) const { 
    return lp->getPrimal((*edge_index_map)[e]);
  }
};

// Use a DIMACS max flow file as stdin.
// max_flow_expresion < dimacs_max_flow_file

int main(int, char **) {

  typedef ListGraph Graph;
  typedef Graph::Node Node;
  typedef Graph::Edge Edge;
  typedef Graph::EdgeIt EdgeIt;

  Graph g;
  
  Node s, t;
  Graph::EdgeMap<int> cap(g);
  readDimacs(std::cin, g, cap, s, t);
  Timer ts;
  
  typedef LPGLPK LPSolver;
  LPSolver lp;
  lp.setMaximize();
  typedef LPSolver::ColIt ColIt;
  typedef LPSolver::RowIt RowIt;
  typedef Graph::EdgeMap<ColIt> EdgeIndexMap;
  typedef Graph::NodeMap<RowIt> NodeIndexMap;
  EdgeIndexMap edge_index_map(g);
  NodeIndexMap node_index_map(g);
  PrimalMap<Edge, EdgeIndexMap> flow(lp, edge_index_map);

  // nonnegativity of flow and capacity function
  for (Graph::EdgeIt e(g); e!=INVALID; ++e) {
    ColIt col_it=lp.addCol();
    edge_index_map.set(e, col_it);
    // interesting property in GLPK:
    // if you change the order of the following two lines, the 
    // two runs of GLPK are extremely different
      lp.setColLowerBound(col_it, 0);
      lp.setColUpperBound(col_it, cap[e]);
  }
  
  for (Graph::NodeIt n(g); n!=INVALID; ++n) {
    LPSolver::Expression expr;
    for (Graph::OutEdgeIt e(g, n); e!=INVALID; ++e)
      expr+=edge_index_map[e];
    for (Graph::InEdgeIt e(g, n); e!=INVALID; ++e)
      expr-=edge_index_map[e];
    // cost function
    if (n==s) {
      lp.setObjCoeffs(expr);      
    }
    // flow conservation constraints
    if ((n!=s) && (n!=t)) {
      RowIt row_it=lp.addRow();
      node_index_map.set(n, row_it);
      lp.setRowCoeffs(row_it, expr);
      lp.setRowLowerBound(row_it, 0.0);
      lp.setRowUpperBound(row_it, 0.0);
//       cout << expr << endl;
//       {
//      LPSolver::Expression expr;
//      lp.getRowCoeffs(node_index_map[n], expr);       
//      cout << expr << endl;
//       }
    }
  }
  lp.solveSimplex();
//   cout << "num of nodes: " << countNodes(g) << endl;
//   cout << "num of edges: " << countEdges(g) << endl;
//   cout << "num of rows: " << lp.rowNum() << endl;
//   cout << "num of rows: " << lp.int_row_map.size() << endl;
//   for (int i=0; i<lp.int_row_map.size(); ++i) {
//     cout << lp.int_row_map[i] << " " << endl;
//   }
//   cout << "num of columns: " << lp.colNum() << endl;
//   cout << "num of columns: " << lp.int_col_map.size() << endl;
//   for (int i=0; i<lp.int_col_map.size(); ++i) {
//     cout << lp.int_col_map[i] << " " << endl;
//   }
  cout << "elapsed time: " << ts << endl;
//   Graph::NodeIt n(g);
//   ++n;
//   for(Graph::OutEdgeIt e(g, n); e!=INVALID; ++e) {
//     cout << edge_index_map[e] << endl;
//   }
//   for(Graph::InEdgeIt e(g, n); e!=INVALID; ++e) {
//     cout << edge_index_map[e] << endl;
//   }
//   LPSolver::DualExpression expr;
//   lp.getRowCoeffs(node_index_map[n], expr);
//   cout << expr << endl;
}