ILOG CPLEX 11.0 User's Manual

◆◆●●at problem modification;at normal termination;from Concert Technology,●●when you call env.endwhen you modify the extracted modelfrom the Callable Library,●when you call a problem modification routine;● when you call CPXfreeprob.If a program terminates abnormally, the files are not removed.Node files could grow very large. Use the parameter TreLim (CPX_PARAM_TRELIM) to limitthe size of the tree so that it does not exceed available disk space, when you chooseNodeFileInd (CPX_PARAM_NODEFILEIND) settings 2 or 3. It is usually better to letILOG CPLEX terminate the run gracefully, with whatever current feasible solution has beenfound, than to trigger an error message or even a program abort.When ILOG CPLEX uses node-file storage, the sequence of nodes processed may differfrom the sequence in which nodes are processed without node-file storage. Nodes innode-file storage are not accessible to user-written callback routines.Change AlgorithmsThe best approach to reduce memory use is to modify the solution process. Here are someways to do so:◆◆Switch the node selection strategy to best estimate, or more drastically to depth-first, asexplained in Table 14.6 on page 268. Depth-first search rarely generates a long,memory-consuming list of unexplored nodes since ILOG CPLEX dives deeply into thetree instead of jumping around. A narrowly focused search, like depth-first, also oftenresults in faster processing times for individual nodes. However, overall solution time isgenerally much worse than with best-bound node selection because each branch issearched exhaustively to its deepest level before it is fathomed in favor of betterbranches.Another memory-conserving strategy is to use strong branching for variable selection;that is, set the parameter VarSel (CPX_PARAM_VARSEL) to the value 3. Strongbranching requires substantial computational effort at each node to decide the bestbranching variable. As a result, it generates fewer nodes and thus makes less overalldemand on memory. Often, strong branching is faster as well.296 ILOG CPLEX 11.0 — USER’ S MANUAL