Gain graph

A gain graph is a graph whose edges are labelled "invertibly", or "orientably", by elements of a group G. This means that, if an edge e in one direction has label g (a group element), then in the other direction it has label g ⁻¹. The label function φ therefore has the property that it is defined differently, but not independently, on the two different orientations, or directions, of an edge e. The group G is called the gain group, φ is the gain function, and the value φ(e) is the gain of e (in some indicated direction). A gain graph is a generalization of a signed graph, where the gain group G has only two elements. See Zaslavsky (1989, 1991).

A gain should not be confused with a weight on an edge, whose value is independent of the orientation of the edge.

Applications

Some reasons to be interested in gain graphs are their connections to network flow theory in combinatorial optimization, to geometry, and to physics.