(a) The friendship network from Zachary's karate club study (26) as described in the text. Nodes associated with the club administrator's faction are drawn as circles, those associated with the instructor's faction are drawn as squares. (b) Hierarchical tree showing the complete community structure for the network calculated by using the algorithm presented in this article. The initial split of the network into two groups is in agreement with the actual factions observed by Zachary, with the exception that node 3 is misclassified. (c) Hierarchical tree calculated by using edge-independent path counts, which fails to extract the known community structure of the network.
