For an
undirected graph, the
degree of a vertex is equal to the number of
adjacent vertices. A special case is a loop, which adds two to the degree. This can be understood by letting each connection of the loop edge count as its own adjacent vertex. In other words, a vertex with a loop "sees" itself as an adjacent vertex from
both ends of the edge thus adding two, not one, to the degree. For a
directed graph, a loop adds one to the
in degree and one to the
out degree. ==See also==