The Linear Programming Solver

Iteration Log for the Network Simplex Algorithm

After finding the embedded network and formulating the appropriate relaxation, the network simplex algorithm uses a primal network simplex algorithm. In the case of a connected network, with one (weakly connected) component, the log will show the progress of the simplex algorithm. The following information is displayed in the iteration log:

Iteration

indicates the iteration number.

PrimalObj

indicates the primal objective value of the current solution.

Primal Infeas

indicates the maximum primal infeasibility of the current solution.

Time

indicates the time spent on the current component by network simplex.

The frequency of the simplex iteration log is controlled by the LOGFREQ= option. The default value of the LOGFREQ= option is 10,000.

If the network relaxation is disconnected, the information in the iteration log shows progress at the component level. The following information is displayed in the iteration log:

Component

indicates the component number being processed.

Nodes

indicates the number of nodes in this component.

Arcs

indicates the number of arcs in this component.

Iterations

indicates the number of simplex iterations needed to solve this component.

Time

indicates the time spent so far in network simplex.

The frequency of the component iteration log is controlled by the LOGFREQ= option. In this case, the default value of the LOGFREQ= option is determined by the size of the network.

The LOGLEVEL= option adjusts the amount of detail shown. By default, LOGLEVEL=MODERATE and reports as in the preceding description. If LOGLEVEL=NONE, no information is shown. If LOGLEVEL=BASIC, the only information shown is a summary of the network relaxation and the time spent solving the relaxation. If LOGLEVEL=AGGRESSIVE, in the case of one component, the log displays as in the preceding description; in the case of multiple components, for each component, a separate simplex iteration log is displayed.