ILOG CPLEX 11.0 User's Manual

Examining the Solution PoolIn the Interactive Optimizer, the command display solution pool produces a synopsisabout the solution pool.Also in the Interactive Optimizer, the command display solution list shows theobjective value of solutions in the pool, along with the percentage of discrete variables thattake a value different from the incumbent. To display all solutions in the pool, usedisplay solution list *. Alternatively, you can specify the indices of the solutions todisplay, for example: display solution list 2-4.The information displayed by both of these commands in the Interactive Optimizer isavailable through methods or routines in Concert Technology and the Callable Library, asshown in Table 15.1.Table 15.1 summarizes methods, routines, and commands that access aggregatedinformation about the solution pool itself, such information as the number of solutions in thepool, the number of solutions that have been replaced, and the arithmetic mean of theobjective value of solutions in the pool.Solutions are replaced, according to the replacement policy, when the pool reaches the limiton its capacity. In the presence of an objective tolerance specific to the solution pool, asspecified either by the relative gap parameter (SolnPoolGap, CPX_PARAM_SOLNPOOLGAP)or by the absolute gap parameter (SolnPoolAGap, CPX_PARAM_SOLNPOOLAGAP), solutionsthat are generated but then deleted because of the improvement in the best integer value arealso counted as replaced.Table 15.1Accessing information about the solution poolPurpose Concert method Callable Library routineInteractive OptimizercommandNumber of solutions getSolnPoolNsolns CPXgetsolnpoolnumsolns display solution poolNumber replaced getSolnPoolNreplaced CPXPgetsolnpoolnumreplaced display solution poolArithmetic mean ofobjective valuesgetSolnPoolMeanObjValue CPXPgetsolnpoolmeanobjval display solution poolAccessing a Solution in the Solution PoolThe solutions in the pool are indexed numerically. The index -1 (minus one) normallyspecifies the incumbent. Generally, low index numbers specify the solutions found early.However, the index numbers may change if you re-populate the pool, depending on thestrategy in use when the pool reaches the limit of its capacity.316 ILOG CPLEX 11.0 — USER’ S MANUAL