The NETFLOW Procedure

Interactivity

PROC NETFLOW can be used interactively. You begin by giving the PROC NETFLOW statement, and you must specify the ARCDATA= data set. The CONDATA= data set must also be specified if the problem has side constraints. If necessary, specify the NODEDATA= data set.

The variable lists should be given next. If you have variables in the input data sets that have special names (for example, a variable in the ARCDATA= data set named _TAIL_ that has tail nodes of arcs as values), it may not be necessary to have many or any variable lists.

The CONOPT, PIVOT, PRINT, QUIT, SAVE, SHOW, RESET, and RUN statements follow and can be listed in any order. The CONOPT and QUIT statements can be used only once. The others can be used as many times as needed.

Use the RESET or SAVE statement to change the names of the output data sets. With RESET, you can also indicate the reasons why optimization should stop (for example, you can indicate the maximum number of stage 1 or stage 2 iterations that can be performed). PROC NETFLOW then has a chance to either execute the next statement, or, if the next statement is one that PROC NETFLOW does not recognize (the next PROC or DATA step in the SAS session), do any allowed optimization and finish. If no new statement has been submitted, you are prompted for one. Some options of the RESET statement enable you to control aspects of the primal simplex algorithm. Specifying certain values for these options can reduce the time it takes to solve a problem. Note that any of the RESET options can be specified in the PROC NETFLOW statement.

The RUN statement starts or resumes optimization. The PIVOT statement makes PROC NETFLOW perform one simplex iteration. The QUIT statement immediately stops PROC NETFLOW. The CONOPT statement forces PROC NETFLOW to consider constraints when it next performs optimization. The SAVE statement has options that enable you to name output data sets; information about the current solution is put in these output data sets. Use the SHOW statement if you want to examine the values of options of other statements. Information about the amount of optimization that has been done and the STATUS of the current solution can also be displayed using the SHOW statement.

The PRINT statement instructs PROC NETFLOW to display parts of the problem. PRINT ARCS produces information on all arcs. PRINT SOME_ARCS limits this output to a subset of arcs. There are similar PRINT statements for nonarc variables and constraints:

  
   print nonarcs; 
   print some_nonarcs; 
   print constraints; 
   print some_cons;
 

PRINT CON_ARCS enables you to limit constraint information that is obtained to members of a set of arcs that have nonzero constraint coefficients in a set of constraints. PRINT CON_NONARCS is the corresponding statement for nonarc variables.

For example, an interactive PROC NETFLOW run might look something like this:

  
   proc netflow arcdata=data set 
         other options; 
      variable list specifications; /* if necessary */ 
      reset options; 
      print options;    /* look at problem                  */ 
      run;              /* do some optimization             */ 
      /* suppose that optimization stopped for  */ 
      /* some reason or you manually stopped it */ 
      print options;    /* look at the current solution     */ 
      save options;     /* keep current solution            */ 
      show options;     /* look at settings                 */ 
      reset options;    /* change some settings, those that */ 
                        /* caused optimization to stop      */ 
      run;              /* do more optimization             */ 
      print options;    /* look at the optimal solution     */ 
      save options;     /* keep optimal solution            */
 

If you are interested only in finding the optimal solution, have used SAS variables that have special names in the input data sets, and want to use default settings for everything, then the following statement is all you need: