lp_demo.cc File Reference

Demo program for the LP solver interface. More...

#include <iostream>
#include <lemon/lp.h>

Detailed Description

This demo program shows how the LEMON LP solver interface can be used. A simple linear programming (LP) problem is formulated and solved using the default LP solver (e.g. GLPK).

/* -*- mode: C++; indent-tabs-mode: nil; -*-
 *
 * This file is a part of LEMON, a generic C++ optimization library.
 *
 * Copyright (C) 2003-2010
 * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport
 * (Egervary Research Group on Combinatorial Optimization, EGRES).
 *
 * Permission to use, modify and distribute this software is granted
 * provided that this copyright notice appears in all copies. For
 * precise terms see the accompanying LICENSE file.
 *
 * This software is provided "AS IS" with no warranty of any kind,
 * express or implied, and with no claim as to its suitability for any
 * purpose.
 *
 */


#include <iostream>
#include <lemon/lp.h>

using namespace lemon;

int main()
{
  // Create an instance of the default LP solver class
  // (it will represent an "empty" problem at first)
  Lp lp;

  // Add two columns (variables) to the problem
  Lp::Col x1 = lp.addCol();
  Lp::Col x2 = lp.addCol();

  // Add rows (constraints) to the problem
  lp.addRow(x1 - 5 <= x2);
  lp.addRow(0 <= 2 * x1 + x2 <= 25);
  
  // Set lower and upper bounds for the columns (variables)
  lp.colLowerBound(x1, 0);
  lp.colUpperBound(x2, 10);
  
  // Specify the objective function
  lp.max();
  lp.obj(5 * x1 + 3 * x2);
  
  // Solve the problem using the underlying LP solver
  lp.solve();

  // Print the results
  if (lp.primalType() == Lp::OPTIMAL) {
    std::cout << "Objective function value: " << lp.primal() << std::endl;
    std::cout << "x1 = " << lp.primal(x1) << std::endl;
    std::cout << "x2 = " << lp.primal(x2) << std::endl;
  } else {
    std::cout << "Optimal solution not found." << std::endl;
  }

  return 0;
}