Solving an optimization problem

The basic search strategy in CP Optimizer can be used to solve optimization problems.

The basic algorithm for solving a model is invoked by calling the method solve, a member function of the optimizer object. (For example, in the C++ API, this is IloCP::solve. In the Java™ API, this method is IloCP.solve. In the C# API, this method is CP.Solve.) This function returns true (IloTrue in the C++ API) when the engine has found an optimal solution. If the model has no objective function, then this call returns true when a solution is found. The function returns false (IloFalse in the C++ API) when the problem has no solution.

Consider the following model with 3 integer variables, written in the C++ API:

    IloIntVar x(env, 0, 7, "x");
    IloIntVar y(env, 0, 7, "y");
    IloIntVar z(env, 0, 7, "z");
    IloIntVarArray all(env, 3, x, y, z);
    model.add(IloMinimize(env, IloSum(all)));
    model.add(IloAllDiff(env, all));
    model.add(y == IloElement(IloIntArray(env, 7, 3, 7, 8, 8, 0, 1, 4), x));

To solve the problem represented by this model, you can call the method IloCP::solve, like this:

    IloCP cp(model);
    cp.setParameter(IloCP::LogVerbosity, IloCP::Quiet);
    if (cp.solve()){
      cp.out() << " An optimal solution has been found" 
               << ", objective value = " << cp.getObjValue()
               << ", x = " << cp.getValue(x)
               << ", y = " << cp.getValue(y)
               << ", z = " << cp.getValue(z) << std::endl;
    } else {
      cp.out() << " The problem has no solution " << std::endl;
    }

In this example, the search log output is deactivated for the sake of brevity. Information regarding the search log is presented in the section The search log. The method getValue, a member function of the optimizer object, takes a decision variable as an argument and returns the value of that variable in the solution that was found. The method getObjValue, a member function of the optimizer object, returns the value of the objective for this solution.

Running this code produces the output:

An optimal solution has been found, objective value = 4, x = 0, y = 3, z = 1

In the C++ API of CP Optimizer, you use the class IloCP and the methods IloCP::solve, IloCP::getValue and IloCP::getObjValue.

In the Java API of CP Optimizer, you use the class IloCP and the methods IloCP.solve, IloCP.getValue and IloCP.getObjValue.

In the C# API of CP Optimizer, you use the class CP and the methods CP.Solve and CP.GetValue and the member CP.ObjValue.