ILOG CPLEX 11.0 User's Manual

memory. It also includes several options to reduce the use of physical memory. Importantly,it entails only a very small increase in runtime. In terms of performance, node-file storageoffers a much better option than relying on generic swap space managed by your operatingsystem.This feature is especially helpful when you are using steepest-edge pricing as thesubproblem simplex pricing strategy because pricing information itself consumes a greatdeal of memory.Note: Try node files whenever the MIP optimizer terminates with the condition "out ofmemory" and the node count is greater than zero. The message in such a situation lookslike the following sample output.Clique cuts applied: 30CPLEX Error 1001: Out of memory.Consider using CPLEX node files to reduce memory usage.MIP-Error termination, integer feasible: Objective = 5.6297000000e+04Current MIP best bound = 5.5731783224e+04 (gap = 565.217, 1.00%)Solution time = 220.75 sec. Iterations = 16707 Nodes = 101 (58)There are several parameters that control the use of node files. They are:◆◆◆WorkMem in Concert Technology or CPX_PARAM_WORKMEM in the Callable LibraryNodeFileInd in Concert Technology or CPX_PARAM_NODEFILEIND in the CallableLibraryTreLim in Concert Technology or CPX_PARAM_TRELIM in the Callable Library◆ WorkDir in Concert Technology or CPX_PARAM_WORKDIR in the Callable LibraryILOG CPLEX uses node file storage most effectively when the amount of working memoryis reasonably large so that it does not have to create node files too frequently. The defaultvalue of the WorkMem parameter is 128 megabytes. Setting it to higher values, even on amachine with very large memory, can be expected to result in only marginally improvedefficiency. However, it is advisable to reduce this setting to approximately half the availablememory of your machine if your machine has less than 256 megabytes of RAM to avoiddefeating the purpose of node files, a situation that would occur if your applicationinadvertently triggers the swap space of your operating system.When tree storage size exceeds the limit defined by WorkMem, and if the tree-memory limithas not been exceeded, then what happens next is decided by the setting of the node fileindicator (NodeFileInd in Concert Technology or CPX_PARAM_NODEFILEIND in the294 ILOG CPLEX 11.0 — USER’ S MANUAL