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=== 规模 ===

=== 规模 ===

The size of a network can refer to the number of nodes <math>N</math> or, less commonly, the number of edges <math>E</math> which (for connected graphs with no multi-edges) can range from <math>N-1</math> (a tree) to <math>E_{\max}</math> (a complete graph). In the case of a simple graph (a network in which at most one (undirected) edge exists between each pair of vertices, and in which no vertices connect to themselves), we have <math>E_{\max}=\tbinom N2=N(N-1)/2</math>; for directed graphs (with no self-connected nodes), <math>E_{\max}=N(N-1)</math>; for directed graphs with self-connections allowed, <math>E_{\max}=N^2</math>. In the circumstance of a graph within which multiple edges may exist between a pair of vertices, <math>E_{\max}=\infty</math>.

The size of a network can refer to the number of nodes <math>N</math> or, less commonly, the number of edges <math>E</math> which (for connected graphs with no multi-edges) can range from <math>N-1</math> (a tree) to <math>E_{\max}</math> (a complete graph). In the case of a simple graph (a network in which at most one (undirected) edge exists between each pair of vertices, and in which no vertices connect to themselves), we have <math>E_{\max}=\tbinom N2=N(N-1)/2</math>; for directed graphs (with no self-connected nodes), <math>E_{\max}=N(N-1)</math>; for directed graphs with self-connections allowed, <math>E_{\max}=N^2</math>. In the circumstance of a graph within which multiple edges may exist between a pair of vertices, <math>E_{\max}=\infty</math>.