The degree of a graph vertex of a graph is the number of graph edges which touch the graph vertex, also called the local degree. The graph vertex degree of a point A in a graph, denoted ρ(A), satisfies sum_(i = 1)^n ρ(A_i) = 2E, where E is the total number of graph edges. Directed graphs have two types of degrees, known as the indegree and outdegree.