Class IloTournamentSelector<,>

A tournament selection is one where objects compete to be selected and therefore a notion of pairwise comparable objects is needed. A tournament selector is defined by two objects: the tournament size (referred to as t) and a comparator. To select an object, the tournament selector selects t objects in a random unbiased way with replacement, meaning that the same object can be selected more than once. Then, the comparator is used to select the best of those t objects. In the case of ties (equal quality objects), the object selected first in the initial round will be chosen. The effect of the tournament size t is to prefer the "better" objects for higher t. t=1 corresponds to random selection, but for normal usage, t is normally a small integer, as if it is too high, only the very best objects are ever selected.

When you create a tournament selector, you must pass a visitor object which can traverse the container from which you are selecting objects. However, in the case where a default visitor exists for the container in question, you can omit the visitor and the default will be used. In addition to the default visitors already in Solver, IIM provides default visitors for IloSolutionPool and IloPoolProcArray.

The following code shows how to declare a tournament selector and use it to build a pool processor:

    IloTournamentSelector<IloSolution, IloSolutionPool> tsel(
      env, 2, IloBestSolutionComparator(env)
    );
    IloPoolProc selector = IloSelectSolutions(env, tsel, IloTrue);

In this example, better objective value solutions are preferred and the tournament size is two.

This constructor builds a selector from an environment env which will select objects according to a competitive "tournament" rule. This constructor uses the comparator cmp to compare objects. The parameter tournamentSize controls the number of randomly chosen objects to consider each time a selection is made. It is used to control the size of the competition and thus the bias of the selector towards preferred objects. An optional visitor visitor can be passed to traverse the container. If no visitor is specified, a default visitor will be used if it exists. If no default visitor exists, an exception of type IloException is raised.

This member function returns the comparator passed at construction time.

This member function returns the tournament size given at construction time.

This member function returns the visitor passed at construction time, or, if no visitor was passed, the default visitor for the container from which objects are being selected.