Directed graph

graph with oriented edges

In graph theory, a directed graph (or digraph) is a graph which has directed edges. This means one end of the edge is different from the other end. Directed edges can be thought of as arrows, or as edges which can only be travelled in one direction.

A directed graph, vertex D cannot be reached from vertex B.

Degree

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For a normal graph, the degree of a vertex   is the number of edges touching  .

For a digraph, there are two more definitions. The indegree of   is the number of edges going into  , and the outdegree of   is the number of edges going out of  .

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