The NETFLOW Procedure

Macro Variable _ORNETFL

The NETFLOW procedure creates and initializes a SAS macro variable called _ORNETFL. After exiting the procedure, you can use %put &_ORNETFL; to view details about the optimization.

When the network simplex method is used, the value of _ORNETFL consists of the following parts:

• ERROR_STATUS, indicating the existence or absence of any errors
• OPT_STATUS, the stage of the optimization, or what solution has been found
• OBJECTIVE=objective, the total cost or profit of the current solution. OBJECTIVE can be followed by or replaced by one of the following:
  • MAXFLOW=maxflow, the amount of the current solution's maximal flow, follows OBJECTIVE= if PROC NETFLOW is solving a maximal flow problem (MAXFLOW specified)
  • MINFLOW=minflow, the amount of the current solution's minimal flow, follows OBJECTIVE= if PROC NETFLOW is solving a minimal flow problem (MAXFLOW and MAXIMIZE specified at the same time)
  • SHORTEST_PATH=shortpath, the length of the shortest path, appears instead of OBJECTIVE= if PROC NETFLOW is solving a shortest path problem (SHORTPATH specified)
  • LONGEST_PATH=longpath, the length of the longest path, appears instead of OBJECTIVE= if PROC NETFLOW is solving a longest path problem (SHORTPATH and MAXIMIZE specified at the same time)
• SOLUTION, describing the nature of the current solution

When the interior point algorithm is used, the value of _ORNETFL consists of the following parts:

• ERROR_STATUS, indicating the existence or absence of any errors
• SOLUTION, describing the nature of the current solution
• OBJECTIVE=objective, the total cost or profit of the current solution. OBJECTIVE can be followed by or replaced by one of the following:
  • MAXFLOW=maxflow, the amount of the current solution's maximal flow, follows OBJECTIVE= if PROC NETFLOW is solving a maximal flow problem (MAXFLOW specified)
  • MINFLOW=minflow, the amount of the current solution's minimal flow, follows OBJECTIVE= if PROC NETFLOW is solving a minimal flow problem (MAXFLOW and MAXIMIZE specified at the same time)
  • SHORTEST_PATH=shortpath, the length of the shortest path, appears instead of OBJECTIVE= if PROC NETFLOW is solving a shortest path problem (SHORTPATH specified)
  • LONGEST_PATH=longpath, the length of the longest path, appears instead of OBJECTIVE= if PROC NETFLOW is solving a longest path problem (SHORTPATH and MAXIMIZE specified at the same time)
• ITERATIONS=n, the number of iterations required to solve the problem
• ITERATING_TIME=Ti, the time in seconds taken by the interior point algorithm to perform iterations for solving the problem
• SOLUTION_TIME=Ts, the time in seconds taken by the procedure to presolve the problem, perform interior point iterations, and postsolve the problem

Ideally, at the end of a PROC NETFLOW run in which the network simplex method is used, _ORNETFL has the following value:

  
    ERROR_STATUS=OK OPT_STATUS=OPTIMAL OBJECTIVE=x 
    SOLUTION=OPTIMAL
 

At the end of a PROC NETFLOW run in which the interior point algorithm is used, _ORNETFL should have the following value:

  
    ERROR_STATUS=OK SOLUTION=OPTIMAL OBJECTIVE=x 
    ITERATIONS=x ITERATING_TIME=x SOLUTION_TIME=x
 

Nontrailing blank characters that are unnecessary are removed.

If the preprocessor detects that a problem with a network component is infeasible, and you specify that the interior point algorithm should be used, _ORNETFL has the following value:

  
   ERROR_STATUS=OK SOLUTION=INFEASIBLE 
   ITERATIONS=0 ITERATING_TIME=0 SOLUTION_TIME=0
 

The same value is assigned to the _ORNETFL macro variable if the preprocessor detects that an LP problem is infeasible.

Table 5.6 lists alternate values for the _ORNETFL value parts.

Table 5.6: PROC NETFLOW _ORNETFL Macro Values

Keyword	Value	Meaning
ERROR_STATUS	OK	no errors
	MEMORY	memory request failed
	IO	input/output error
	DATA	error in the data
	BUG	error with PROC NETFLOW
	SEMANTIC	semantic error
	SYNTAX	syntax error
	UNKNOWN	unknown error
OPT_STATUS	START	no optimization has been done
	STAGE_1	performing stage 1 optimization
	UNCON_OPT	reached unconstrained optimum, but there are side constraints
	STAGE_2	performing stage 2 optimization
	OPTIMAL	reached the optimum
OBJECTIVE	objective	total cost or profit
MINFLOW	minflow	if MAXFLOW and MAXIMIZE are specified at the same time
MAXFLOW	maxflow	if MAXFLOW is specified
SHORTEST_PATH	shortpath	if SHORTPATH is specified
LONGEST_PATH	longpath	if SHORTPATH and MAXIMIZE are specified at the same time
SOLUTION	NONOPTIMAL	more optimization is required
	STAGE_2_REQUIRED	reached unconstrained optimum, stage 2 optimization is required
	OPTIMAL	have determined the optimum
	INFEASIBLE	infeasible; no solution exists
	UNRESOLVED_OPTIMALITY _OR_FEASIBILITY	the optimization process stops before optimality or infeasibility can be proven.
	MAXITERB_OPTION _STOPPED_OPTIMIZATION	the interior point algorithm stops after performing maximal number of iterations specified by the MAXITERB= option