The NETFLOW Procedure

The NETFLOW procedure for network flow optimization contains a new feature that enables you to specify and solve generalized network problems. In generalized networks, the amount of flow that enters an arc might not equal the amount of flow that leaves the arc, signifying a loss or a gain as flow traverses the arc. A new PROC NETFLOW option, GENNET, indicates that the network is generalized. Generalized networks have a broad range of practical applications, including the following:

• transportation of perishable goods (weight loss due to drying)

• financial investment account balances (interest rates)

• manufacturing (yield ratios)

• electrical power generation (loss during transmission along lines)

Another new option, EXCESS=, enables you to use PROC NETFLOW to solve an even wider variety of network flow optimization problems for both standard and generalized networks. As a result, PROC NETFLOW is equipped to deal with many frequently encountered challenges to successful network flow optimization, such as the following:

• networks with excess supply or demand

• networks that contain nodes with unknown supply and demand values

• networks with nodes that have range constraints on supply and demand

In SAS/OR 9.2, the MPSOUT= option directs the NETFLOW procedure to save input problem data in an MPS-format SAS data set. Invoking the MPSOUT= option causes the NETFLOW procedure to output the data and halt without attempting optimization. The MPS-format SAS data set corresponds closely to the MPS-format text file (commonly used in the optimization community). Problems that are specified in this format can be solved by using the OPTLP procedure.