Types of Vertices in a Digraph

Topics: Graph Theory - Internal and External Degrees of a Vertex - Vertex - Digraph

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(definition)

In a digraph, vertices can be of several types:

• We say that a vertex is isolated if the sum of its external and internal degrees is equal to $0$.

• A final (or terminal) vertex is a vertex whose external degree is $0$.

• An initial vertex is a vertex whose internal degree is $0$ and whose external degree is not $0$.

• A hanging vertex is a vertex whose sum of external and internal degrees is $1$.