A model is just a set of modeling objects of type IloAddable such as IloObjective and IloRange. Objects of classes implementing this interface can be added to an instance of IloModel. Other IloAddable objects usable with IloCplex are IloLPMatrix, IloConversion, IloSOS1, and IloSOS2. These will be covered in the IloMPModeler section.

Variables cannot be added to a model because IloNumVar is not an extension of IloAddable. All variables used by other modeling objects (IloAddable objects) that have been added to a model are implicitly part of this optimization model. The explicit addition of a variable to a model can thus be avoided.

During modeling, a typical sequence of operations is to create a modeling object and immediately add it to the active model. To facilitate this, for most constructors with a name such as ConstructorName, there is also a method addConstructorName which immediately adds the newly constructed modeling object to the active model. For example, the call

  IloObjective obj = cplex.addMaximize(expr);

is equivalent to

  IloObjective obj = cplex.add(cplex.maximize(expr));

Not only do the addConstrucorName methods simplify the program, they are also more efficient than the two equivalent calls because an intermediate copy can be avoided.