The TAILNODE statement specifies the SAS variable that must (when solving an NPSC problem) be present in the ARCDATA=
data set that has as values the names of tail nodes of arcs. The TAILNODE variable must have character values. It is not
necessary to have a TAILNODE statement if the name of the SAS variable is _TAIL_
or _FROM_
. If the TAILNODE list variable value is missing, it is assumed that the observation of the ARCDATA=
data set contains information concerning a nonarc variable. There should be no TAILNODE statement if you are solving an LP.