Bidirected graph

In the mathematical domain of graph theory, a bidirected graph (introduced by Edmonds & Johnson 1970)[1] is a graph in which each edge is given an independent orientation (or direction, or arrow) at each end.

Thus, there are three kinds of bidirected edges: those where the arrows point outward, towards the vertices, at both ends; those where both arrows point inward, away from the vertices; and those in which one arrow points away from its vertex and towards the opposite end, while the other arrow points in the same direction as the first, away from the opposite end and towards its own vertex.

Edges of these three types may be called, respectively, extraverted, introverted, and directed.

It is sometimes desirable to have also edges with only one end (half-edges); these get only one arrow.

This graph theory-related article is a stub.