We introduce a cyclic coefficient $R$ which characterizes the degree of circulation in complex networks. If a network has a perfect treelike structure, then $R$ becomes zero. The larger value of $R$ represents that the network has more cyclic structure. We measure both the cyclic coefficients and the distributions of local cyclic coefficients for various networks and discuss the cyclic structures of them.

• Received 14 November 2004

DOI:https://doi.org/10.1103/PhysRevE.72.036109