Graph (discrete mathematics): Difference between revisions

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A [[multigraph]] is a generalization that allows multiple edges to have the same pair of endpoints. In some texts, multigraphs are simply called graphs.{{sfn|Bender|Williamson|2010|p=149}}<ref>Graham et al., p. 5.</ref>
 
Sometimes, graphs are allowed to contain ''[[Loop (graph theory)|loop]]s'', which are edges that join a vertex to itself. To allow loops, the pairs of vertices in {{mvar|E}} must be allowed to have the same node twice. Such generalized graphs are simply called ''graphs with loops'' or simply ''graphs'' when it is clear from the context that loops are allowed.
 
Generally, the vertex set {{mvar|V}} is taken to be finite (which implies that the edge set {{mvar|E}} is also finite). Sometimes [[infinite graph]]s are considered, but they are usually viewed as a special kind of [[binary relation]], because most results on finite graphs either do not extend to the infinite case or need a rather different proof.