ILOG CPLEX 11.0 User's Manual

Parameters of the Solution PoolILOG CPLEX provides parameters to control the solution pool. Table 15.3 summarizesthese parameters. ILOG CPLEX Parameter Reference Manual documents each of theseparameters in greater detail.Table 15.3 Parameters for the solution poolPurpose Concert parameter Callable Library parameter Interactive OptimizerIntensity SolnPoolIntensity CPX_PARAM_SOLNPOOLINTENSITY mip pool intensityLimit on pool (number ofsolutions generated)Limit on capacity(number of solutionsstored)PopulateLim CPX_PARAM_POPULATELIM mip limits populateSolnPoolCapacity CPX_PARAM_SOLNPOOLCAPACITY mip pool capacityReplacement strategy SolnPoolReplace CPX_PARAM_SOLNPOOLREPLACE mip pool replaceRelative objective gap SolnPoolGap CPX_PARAM_SOLNPOOLGAP mip pool relgapAbsolute objective gap SolnPoolAGap CPX_PARAM_SOLNPOOLAGAP mip pool absgapThe node limit parameter (NodeLim, CPX_PARAM_NODELIM) and time limit parameter(TiLim, CPX_PARAM_TILIM) also have an effect on the solution pool, just as they influenceMIP optimization generally. For more detail about these parameters, see their entries in theILOG CPLEX Parameter Reference Manual.Example: Quality Control through the Solution Pool Gap ParameterIn many cases, solutions are interesting only if their objective value is close to the optimalobjective value of the model. In that context, you can control the quality of solutionsgenerated and saved in the solution pool with the solution pool absolute gap parameter(SolnPoolAGap, CPX_PARAM_SOLNPOOLAGAP) and the solution pool relative gapparameter (SolnPoolGap, CPX_PARAM_SOLNPOOLGAP).To demonstrate this idea, consider again the example cited in Example: Simple FacilityLocation Problem on page 302. In order to obtain solutions that are less than 10% worsethan the optimal objective value, specify the solution pool relative gap parameter in theInteractive Optimizer like this:read location.lpset mip pool relgap 0.1populateILOG CPLEX 11.0 — USER’ S MANUAL 321