ILOG CPLEX 11.0 User's Manual

of the objective function calculated in terms of these modified objective coefficients inparentheses in the network log file.You can control the amount of information recorded in the network log file, just as youcontrol the amount of information in other ILOG CPLEX log files. To record no informationat all in the log file, use the command set network display 0. To display the currentobjective value in parentheses relative to the actual unmodified objective coefficients, usethe command set network display 1. To see the display mentioned earlier in thissection, leave the network display parameter at its default value, 2. (If you have changed thedefault value, you can reset it with the command set network display 2.)Tuning Performance of the Network OptimizerThe default values of parameters controlling the network optimizer are generally the bestchoices for effective performance. However, the following sections indicate parameters thatyou may want to experiment with in your particular problem.Controlling ToleranceYou control the feasibility tolerance for the network optimizer through the parameterNetEpRHS. Likewise, you control the optimality tolerance for the network optimizer throughthe parameter NetEpOpt.Selecting a Pricing Algorithm for the Network OptimizerOn the rare occasions when the network optimizer seems to take too long to find a solution,you may want to change the pricing algorithm to try to speed up computation. The pricingalgorithm for the network optimizer is controlled by parameter NetPPriInd. All thechoices use variations of partial reduced-cost pricing.Limiting Iterations in the Network OptimizerUse the parameter NetItLim if you want to limit the number of iterations that the networkoptimizer performs.Solving Problems with the Network OptimizerYou instruct ILOG CPLEX to apply the network optimizer for solving the LP at hand bysetting the CPX_PARAM_LPMETHOD parameter to CPX_ALG_NET in the Callable Library, orby setting the RootAlg parameter to Network in Concert Technology. When you do so,ILOG CPLEX performs a sequence of steps. It first searches for a part of the LP thatconforms to network structure. Such a part is known as an embedded network. It then usesthe network optimizer to solve that embedded network. Next, it uses the resulting basis toconstruct a starting basis for the full LP problem. Finally, it solves the LP problem with asimplex optimizer.ILOG CPLEX 11.0 — USER’ S MANUAL 221