directed graph

A directed graphMathworldPlanetmath or digraph is a pair G=(V,E) where V is a set of vertices and E is a subset of V×V called edges or arcs.

If E is symmetricMathworldPlanetmathPlanetmath (i.e., (u,v)E if and only if (v,u)E), then the digraph is isomorphicPlanetmathPlanetmath to an ordinary (that is, undirected) graph.

Digraphs are generally drawn in a similarMathworldPlanetmathPlanetmath manner to graphs with arrows on the edges to indicate a sense of direction. For example, the digraph


may be drawn as