The INTPOINT Procedure
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Overview
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Getting Started
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SyntaxFunctional SummaryDictionary of OptionsPROC INTPOINT StatementCAPACITY StatementCOEF StatementCOLUMN StatementCOST StatementDEMAND StatementHEADNODE StatementID StatementLO StatementNAME StatementNODE StatementQUIT StatementRHS StatementROW StatementRUN StatementSUPDEM StatementSUPPLY StatementTAILNODE StatementTYPE StatementVAR Statement
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DetailsInput Data SetsOutput Data SetsConverting Any PROC INTPOINT Format to an MPS-Format SAS Data SetCase SensitivityLoop ArcsMultiple ArcsFlow and Value BoundsTightening Bounds and Side ConstraintsReasons for InfeasibilityMissing S Supply and Missing D Demand ValuesBalancing Total Supply and Total DemandHow to Make the Data Read of PROC INTPOINT More EfficientStopping Criteria
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ExamplesProduction, Inventory, Distribution ProblemAltering Arc DataAdding Side ConstraintsUsing Constraints and More Alteration to Arc DataNonarc Variables in the Side ConstraintsSolving an LP Problem with Data in MPS FormatConverting to an MPS-Format SAS Data SetMigration to OPTMODEL: Production, Inventory, Distribution
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Flow and Value Bounds
The capacity and lower flow bound of an arc can be equal. Negative arc capacities and lower flow bounds are permitted. If
both arc capacities and lower flow bounds are negative, the lower flow bound must be at least as negative as the capacity.
An arc (A,B) that has a negative flow of 
units can be interpreted as an arc that conveys f units of flow from node B to node A.
The upper and lower value bound of a nonarc variable can be equal. Negative upper and lower bounds are permitted. If both are negative, the lower bound must be at least as negative as the upper bound.
When solving an LP, the upper and lower value bounds of an LP variable can be equal. Negative upper and lower bounds are permitted. If both are negative, the lower bound must be at least as negative as the upper bound.
In short, for any problem to be feasible, a lower bound must be 
the associated upper bound.