
Theoretical efforts have been made to study the nontrivial properties of complex networks, such as clustering, scalefree degree distribution, community structures, etc. Here Reciprocity is another quantity to specifically characterize directed networks. Link reciprocity measures the tendency of vertex pairs to form mutual connections between each other. == Motivation == In real network problems, people are interested in determining the likelihood of occurring double links (with opposite directions) between vertex pairs. This problem is fundamental for several reasons. First, in the networks that transport information or material (such as email networks,〔M. E. J. Newman, S. Forrest, and J. Balthrop, Phys. Rev. E 66, 035101(R) (2002).〕 World Wide Web (WWW),〔R. Albert, H. Jeong, and A.L. Baraba´si, Nature (London) 401, 130 (1999).〕 World Trade Web,〔D. Garlaschelli and M. I. Loffredo, Phys. Rev. Lett. 93, 188701 (2004).〕 or Wikipedia〔V. Zlatic, M. Bozicevic, H. Stefancic, and M. Domazet, Phys. Rev. E 74, 016115 (2006)〕 ), mutual links facilitate the transportation process. Second, when analyzing directed networks, people often treat them as undirected ones for simplicity; therefore, the information obtained from reciprocity studies helps to estimation the error introduced when a directed network is treated as undirected (for example, when measuring the clustering coefficient). Finally, detecting nontrivial patterns of reciprocity can reveal possible mechanisms and organizing principles that shape the observed network's topology.〔 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「Reciprocity (network science)」の詳細全文を読む スポンサード リンク
