Example ilolpex6.cpp

The example, ilolpex6.c, resembles one you may have studied in the manual Getting Started with ILOG CPLEX, ilolpex1.c. This example differs from that earlier one in these ways:

Arrays are constructed using the populatebyrow method, and thus no command line arguments are needed to select a construction method.
In the main routine, the arrays cstat and rstat set the status of the initial basis.
After the problem data has been copied into the problem object, the basis is copied by a call to cplex.getStatuses().
After the problem has been optimized, the iteration count is printed. For the given data and basis, the basis is optimal, so no iterations are required to optimize the problem.

The main program starts by declaring the environment and terminates by calling method end() for the environment. The code in between is encapsulated in a try block that catches all Concert Technology exceptions and prints them to the C++ error stream cerr. All other exceptions are caught as well, and a simple error message is issued. Next the model object and the cplex object are constructed. The function populatebycolumn() builds the problem object and, as we noted earlier, cplex.getStatuses() copies the advanced starting basis.

Complete Program

The complete program, ilolpex6.cpp, appears here or online in the standard distribution

#include <ilcplex/ilocplex.h>
ILOSTLBEGIN


static void
   populatebycolumn (IloModel model, IloNumVarArray var, IloRangeArray rng);

int
main (int argc, char **argv)
{
   IloEnv   env;
   try {
      IloModel model(env, "example");

      IloNumVarArray var(env);
      IloRangeArray  rng(env);
      populatebycolumn (model, var, rng);

      IloCplex cplex(model);

      IloCplex::BasisStatusArray cstat(env), rstat(env);
      cstat.add(IloCplex::AtUpper);
      cstat.add(IloCplex::Basic);
      cstat.add(IloCplex::Basic);
      rstat.add(IloCplex::AtLower);
      rstat.add(IloCplex::AtLower);
      cplex.setStatuses(cstat, var, rstat, rng);
      cplex.solve();

      cplex.out() << "Solution status = " << cplex.getStatus() << endl;
      cplex.out() << "Solution value  = " << cplex.getObjValue() << endl;
      cplex.out() << "Iteration count = " << cplex.getNiterations() << endl;

      IloNumArray vals(env);
      cplex.getValues(vals, var);
      env.out() << "Values        = " << vals << endl;
      cplex.getSlacks(vals, rng);
      env.out() << "Slacks        = " << vals << endl;
      cplex.getDuals(vals, rng);
      env.out() << "Duals         = " << vals << endl;
      cplex.getReducedCosts(vals, var);
      env.out() << "Reduced Costs = " << vals << endl;

      cplex.exportModel("lpex6.lp");
   }
   catch (IloException& e) {
      cerr << "Concert exception caught: " << e << endl;
   }
   catch (...) {
      cerr << "Unknown exception caught" << endl;
   }

   env.end();
   return 0;
}  // END main


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

   IloObjective obj = IloMaximize(env);
   c.add(IloRange(env, -IloInfinity, 20.0));
   c.add(IloRange(env, -IloInfinity, 30.0));

   x.add(IloNumVar(obj(1.0) + c[0](-1.0) + c[1]( 1.0), 35.0, 40.0));
   x.add(obj(2.0) + c[0]( 1.0) + c[1](-3.0));
   x.add(obj(3.0) + c[0]( 1.0) + c[1]( 1.0));

   model.add(obj);
   model.add(c);

}  // END populatebycolumn