ILOG CPLEX 11.0 User's Manual

solution; but examination of solution logs might prove confusing if this behavior is not takeninto account.Dependency Checking in PresolveThe ILOG CPLEX preprocessor offers a dependency checker which strengthens problemreduction by detecting redundant constraints. Such reductions are usually most effectivewith the barrier optimizer, but these reductions can be applied to all types of problems: LP,QP, QCP, MIP, MIQP, MIQCP. Table 9.3 shows you the possible settings of DepInd, theparameter that controls dependency checking, and indicates their effects.Table 9.3 Dependency Checking Parameter DepInd or CPX_PARAM_DEPINDSetting Effect-1 automatic: let CPLEX choose when to use dependency checking0 turn off dependency checking (default)1 turn on only at the beginning of preprocessing2 turn on only at the end of preprocessing3 turn on at beginning and at end of preprocessingFinal Factor after PresolveWhen presolve makes changes to the model prior to optimization, a reverse operation(uncrush) occurs at termination to restore the full model with its solution. With defaultsettings, the simplex optimizers will perform a final basis factorization on the full modelbefore terminating. If you turn on the MemoryEmphasis (bool)(CPX_PARAM_MEMORYEMPHASIS (int) in the Callable Library) parameter to conservememory, the final factorization after uncrushing will be skipped; on large models this cansave some time, but computations that require a factorized basis after optimization (forexample the computation of the condition number Kappa) may be unavailable depending onthe operations presolve performed.Factorization can easily be performed later by a call to a simplex optimizer with theparameter AdvInd set to a value greater than or equal to one.Memory Use and PresolveTo reduce memory use, presolve may compress the arrays used for storage of the originalmodel. This compression can make more memory available for the optimizer that the userhas called. To conserve memory, you can also turn on the MemoryEmphasis (bool)(CPX_PARAM_MEMORYEMPHASIS (int) in the Callable Library) parameter.Controlling Passes in PreprocessingIn rare instances, a user may wish to specify the number of analysis passes that the presolveror the aggregator makes through the problem. The parameters PrePass and AggInd,ILOG CPLEX 11.0 — USER’ S MANUAL 177