# degreeIn -- returns the "in-degree" of a vertex in a digraph

## Synopsis

• Usage:
x = degreeIn (D, v)
• Inputs:
• D, an instance of the type Digraph,
• v, , a vertex of D
• Outputs:

## Description

In a directed graph, we define the degree into a vertex or the "in-degree" of a vertex to be the number of parents of that vertex. Intuitively, this give the number of edges that point into the vertex.

 i1 : D = digraph({1,2,3,4},{{1,2},{2,3},{3,4},{4,2}}); i2 : degreeIn(D, 2) o2 = 2