Example: Optimizing a Basic MIP Problem

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Example: Optimizing a Basic MIP Problem

This example illustrates how to optimize a MIP with the ILOG CPLEX Component Libraries.

Complete Program: ilomipex1.cpp

The example derives from ilolpex8.cpp. Here are the differences between that linear program and this mixed integer program:

The problem to solve is slightly different. It appears in Stating a MIP Problem.
The routine populatebyrow added the variables, objective, and constraints to the model created by the method IloModel model(env).

// File: examples/src/ilomipex1.cpp 
// Version 9.0    
// --------------------------------------------------------------------------
//  Copyright (C) 1999-2003 by ILOG.
//  All Rights Reserved.
//  Permission is expressly granted to use this example in the
//  course of developing applications that use ILOG products.
// --------------------------------------------------------------------------
//
// ilomipex1.cpp - Entering and optimizing a MIP problem

#include <ilcplex/ilocplex.h>

ILOSTLBEGIN

static void
   populatebyrow(IloModel model, IloNumVarArray var, IloRangeArray con);

int
main (void) {
   IloEnv env;
   try {
      IloModel model(env);

      IloNumVarArray var(env);
      IloRangeArray con(env);
      populatebyrow (model, var, con);

      IloCplex cplex(model);
      cplex.solve();

      env.out() << "Solution status = " << cplex.getStatus() << endl;
      env.out() << "Solution value  = " << cplex.getObjValue() << endl;

      IloNumArray vals(env);
      cplex.getValues(vals, var);
      env.out() << "Values        = " << vals << endl;
      cplex.getSlacks(vals, con);
      env.out() << "Slacks        = " << vals << endl;

      cplex.exportModel("mipex1.lp");
   }
   catch (IloException& e) {
      cerr << "Concert exception caught: " << e << endl;
   }
   catch (...) {
      cerr << "Unknown exception caught" << endl;
   }

   env.end();
   return 0;

}  // END main


static void
populatebyrow (IloModel model, IloNumVarArray x, IloRangeArray c)
{
   IloEnv env = model.getEnv();

   x.add(IloNumVar(env, 0.0, 40.0));
   x.add(IloNumVar(env));
   x.add(IloNumVar(env));
   x.add(IloNumVar(env, 2.0, 3.0, ILOINT));
   model.add(IloMaximize(env, x[0] + 2 * x[1] + 3 * x[2] + x[3]));

   c.add( - x[0] +     x[1] + x[2] + 10 * x[3] <= 20);
   c.add(   x[0] - 3 * x[1] + x[2]             <= 30);
   c.add(              x[1]        - 3.5* x[3] == 0);
   model.add(c);

}  // END populatebyrow

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