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In mathematics, and more specifically in graph theory, a multigraph is a graph which is permitted to have multiple edges (also called ''parallel edges''〔For example, see Balakrishnan 1997, p. 1 or Chartrand and Zhang 2012, p. 26.〕), that is, edges that have the same end nodes. Thus two vertices may be connected by more than one edge. There are two distinct notions of multiple edges: * ''Edges without own identity'': The identity of an edge is defined solely by the two nodes it connects. In this case, the term "multiple edges" means that the same edge can occur several times between these two nodes. * ''Edges with own identity'': Edges are primitive entities just like nodes. When multiple edges connect two nodes, these are different edges. A multigraph is different from a hypergraph, which is a graph in which an edge can connect any number of nodes, not just two. For some authors, the terms ''pseudograph'' and ''multigraph'' are synonymous. For others, a pseudograph is a multigraph with loops. ==Undirected multigraph (edges without own identity)== A multigraph ''G'' is an ordered pair ''G'':=(''V'', ''E'') with *''V'' a set of ''vertices'' or ''nodes'', *''E'' a multiset of unordered pairs of vertices, called ''edges'' or ''lines''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Multigraph」の詳細全文を読む スポンサード リンク
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