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Multigraph

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A multigraph is a graph in which we allow multiple edges between two fixed vertices. Formally, a multigraph M is a pair M = (V, E) where V is a (usually finite) set of vertices and E is a (also usually finite) multiset of pairs of elements of V. Frequently in the context of multigraphs one considers graphs where loops are allowed, i.e. E is allowed to contain (possibly several copies of) the pair \{v, v\} for some v \in V.


Generalizations

Multigraphs may be thought of as special cases of (edge-)weighted graphs, where the weight on each edge is the multiplicity of the edge in E. In this interpretation, multigraphs are exactly those weighted graphs for which each edge weight is a positive (or nonnegative) integer.


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