Files stndrd<n>.net contain instances of the
assignment problem with 400 nodes generated as minimum cost
flow networks by use of the NETGEN program (by A. Löbel,
ZIB), see D. Klingman, A. Napier, and J. Stutz:
NETGEN: A program for generating large scale capacitated assignment, transportation and minimum cost flow networks,
Management Science 20 (1974), pp. 814-820.