The SAS variable in this list, which must be present in the NODEDATA= data set, contains supply and demand information for the nodes in the NODE list. A positive SUPDEM list variable value denotes that the node named in the NODE list variable can supply units of flow. A negative SUPDEM list variable value means that this node demands units of flow. If a SAS variable is not explicitly specified, a SAS variable with the name _SUPDEM_ or _SD_ in the NODEDATA= data set is used as the SUPDEM variable. If a node is a transshipment node (neither a supply nor a demand node), an observation associated with this node need not be present in the NODEDATA= data set. If present, the SUPDEM list variable value must be zero or a missing value.