A characterization of network representable polymatroids

Meggido showed that the maximum flow through sets of sources in a multiple sink flow network is a polymatroidal function. Recently, Federgruen and Groenevelt have considered polymatroids that can be represented by a multiple source flow network and have improved the running time of an important scheduling application. The authors give a characterization of network representability and relate representable polymatorids to the theory of gammoids.