Defining a constructive strategy

A constructive strategy can be defined using search phases. A search phase specifies the criteria for the order in which variables and values are chosen in the search.

In addition to variables, a search phase can be used to tune a search strategy by specifying the criteria for the order in which decision variables are chosen to be fixed and to which values these variables should be fixed. This strategy is then used as a constructive strategy to instantiate the decision variables of the phase.

In the C++ API, the constructor of a complete phase is:


  IloSearchPhase(IloIntVarArray x, 
                 IloIntVarChooser varChooser, 
                 IloIntValueChooser valueChooser);

The variable chooser (IloIntVarChooser in the C++ API and the Java™ API, IIntVarChooser in the C# API) defines how the next decision variable to fix in the search is chosen.

The value chooser (IloIntValueChooser in the C++ API and the Java API, IIntValueChooser in the C# API) defines how values are chosen for instantiating decision variables.

Note:

Search phase

A search phase is an object that is used to define instantiation strategies to help the CP Optimizer search. A search phase is composed of

an array of decision variables to instantiate (or fix),
a variable chooser that defines how the next variable to instantiate is chosen
a value chooser that defines how values are chosen when instantiating variables.

Since V12.8, the IloCPEngine class is used in evaluators used by choosers. It provides access to the extracted model objects. See details about IloCPEngine in the CP Optimizer reference manuals.