ILOG CPLEX 11.0 User's Manual

not correct that problem either. In short, the tuning tool does not magically eliminate allperformance bottlenecks. However, if you understand the performance issues of your model,the tuning tool can help you discern parameter settings that lead to faster solving time.The recommended practice with the tuning tool is to solve your model first with defaultsettings and to consider the results before invoking the tuning tool. Your analysis of thoseresults directs you toward the next step. The following sections sketch typical scenarios forworking effectively with the tuning tool and outline what to expect from the tuing tool.◆ If ILOG CPLEX Solves Your Problem to Optimality on page 162◆ If ILOG CPLEX Finds Solutions But Does Not Prove Optimality on page 162◆ Tuning and Time Limits on page 163◆ Tuning Results on page 163If ILOG CPLEX Solves Your Problem to OptimalityIf ILOG CPLEX solves your problem to optimality, you may still want to apply the tuningtool to discover whether you can solve the model faster. In such a case, bear in mind that thetuning tool performs several optimization runs as it goes about its work. These optimizationruns may take six to eight times longer than the default run that produced your optimalresults. If that projected time (six to eight times longer than the initial default run) seems toolong for your purpose, then consider setting a general time limit by means of the parameterTiLim, CPX_PARAM_TILIM or consider setting a specific tuning time limit per problem, peroptimization, by means of the parameter TuningTiLim, CPX_PARAM_TUNINGTILIM.Example: Time Limits on Tuning in the Interactive Optimizer on page 164 illustrates thisapproach through time limits more fully.If ILOG CPLEX Finds Solutions But Does Not Prove OptimalityIn the case where ILOG CPLEX finds solutions for your model but does not proveoptimality in your initial run before invoking the tuning tool, you will likely want to set thetime limit per model. See Tuning and Time Limits on page 163 for more about that idea.In situations where ILOG CPLEX does not solve your model to optimality for a reason otherthan a time limit, you should address that reason before you apply the tuning tool.For example, if your initial run results in an out-of-memory error, consider setting thememory emphasis parameter (MemoryEmphasis (bool), CPX_PARAM_MEMORYEMPHASIS(int)). Then create a file in which you specify a fixed setting of that parameter for thetuning tool to respect. Pass that file to the tuning tool with your model. Fixing Parametersand Tuning Multiple Models in the Interactive Optimizer on page 165 illustrates thisapproach.162 ILOG CPLEX 11.0 — USER’ S MANUAL