ILOG CPLEX 11.0 User's Manual

Solving the ModelOnce you have created an optimization problem in your active model, the IloCplex objectis ready to solve it. This is done, for a model represented by cplex by calling:cplex.solve();The solve method returns a Boolean indicating whether or not a feasible solution was foundand can be queried. However, when true is returned, the solution that was found may not bethe optimal one; for example the optimization may have terminated prematurely because itran into an iteration limit.Additional information about a possible solution available in the IloCplex object can bequeried with the method getStatus returning an IloCplex.Status object. Possiblestatuses are summarized in Table 2.2.Table 2.2 Solution StatusReturn StatusErrorUnknownFeasibleBoundedOptimalInfeasibleUnboundedActive ModelIt has not been possible to process the active model, or anerror occurred during the optimization.It has not been possible to process the active model farenough to prove anything about it. A common reason may bethat a time limit was reached.A feasible solution for the model has been proven to exist.It has been proven that the active model has a finite bound inthe direction of optimization. However, this does not imply theexistence of a feasible solution.The active model has been solved to optimality. The optimalsolution can be queried.The active model has been proven to possess no feasiblesolution.The active model has been proven to be unbounded. Thenotion of unboundedness adopted by IloCplex istechnically that of dual infeasibility; this does not include thenotion that the model has been proven to be feasible.Instead, what has been proven is that if there is a feasiblesolution with objective value z*, there exists a feasiblesolution with objective value z*-1 for a minimization problem,or z*+1 for a maximization problem.InfeasibleOrUnbounded The active model has been proven to be infeasible orunbounded.ILOG CPLEX 11.0 — USER’ S MANUAL 81