| The NETFLOW Procedure |
Flow Conservation Constraints
The constraints 
are referred to as the
nodal flow conservation constraints.
These constraints algebraically state
that the sum of the flow through arcs directed toward a node
plus that node's supply, if any, equals the sum of the flow through arcs
directed away from that node plus that node's demand, if any.
The flow conservation constraints are implicit in
the network model and should not be specified explicitly
in side constraint data when using PROC NETFLOW. The constrained
problems most amenable to being solved by the NETFLOW procedure
are those that,
after the removal of the flow conservation constraints, have very
few constraints. PROC NETFLOW is superior to linear programming
optimizers when the network part of the problem is significantly
larger than the nonnetwork part.
The NETFLOW procedure can also
be used to solve an unconstrained network problem,
that is, one in which 
, 
,
, 
, and 
do not exist.
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