Examining the solution pool

Describes access to generic information about the solution pool.

In the Interactive Optimizer, the command display solution pool produces a synopsis about the solution pool, such as the following lines.


CPLEX> display solution pool
Solution pool: 29 solutions saved.
Mean objective = 5.7372413793e+002

Also in the Interactive Optimizer, the command display solution list shows the objective value of solutions in the pool, along with the percentage of discrete variables that take a value different from the incumbent. To display all solutions in the pool, use display solution list * . Alternatively, you can specify the indices of the solutions to display, for example: display solution list 2-4 .

The information displayed by both of these commands in the Interactive Optimizer is available through methods or routines in Concert Technology and the Callable Library, as shown in Table 1.

Table 1 summarizes methods, routines, and commands that access aggregated information about the solution pool itself, such information as the number of solutions in the pool, the number of solutions that have been replaced, and the arithmetic mean of the objective value of solutions in the pool.

Solutions are replaced, according to the replacement policy, when the pool reaches its maximum capacity. Its maximum capacity is specified by the solution pool capacity parameter (maximum number of solutions kept in solution pool: SolnPoolCapacity, CPX_PARAM_SOLNPOOLCAPACITY) not by the parameter that limits populate (maximum number of solutions generated for solution pool by populate: PopulateLimit, CPX_PARAM_POPULATELIM).

In the presence of an objective tolerance specific to the solution pool, as specified either by the relative gap for solution pool parameter (SolnPoolGap, CPX_PARAM_SOLNPOOLGAP) or by the absolute gap for solution pool parameter (SolnPoolAGap, CPX_PARAM_SOLNPOOLAGAP), solutions that are generated but then deleted because of the improvement in the best integer value are also counted as replaced.

Table 1. Accessing information about the solution pool
Purpose	Concert Technology	Callable Library	Interactive Optimizer
Number of solutions	`getSolnPoolNsolns`	`CPXgetsolnpoolnumsolns`	`display solution pool`
Number replaced	`getSolnPoolNreplaced`	`CPXgetsolnpoolnumreplaced`	`display solution pool`
Arithmetic mean of objective values	`getSolnPoolMeanObjValue`	`CPXgetsolnpoolmeanobjval`	`display solution pool`