From Louvain to Leiden: guaranteeing well-connected communities V.A. Traag,∗ L. Waltman, and N.J. van Eck Centre for Science and Technology Studies, Leiden University, the Netherlands (Dated: October 31, 2019) Community detection is often used to understand...
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From Louvain to Leiden: guaranteeing well-connected communities V.A. Traag,∗ L. Waltman, and N.J. van Eck Centre for Science and Technology Studies, Leiden University, the Netherlands (Dated: October 31, 2019) Community detection is often used to understand the structure of large and complex networks. One of the most popular algorithms for uncovering community structure is the so-called Louvain algorithm. We show that this algorithm has a major defect that largely went unnoticed until now: the Louvain algorithm may yield arbitrarily badly connected communities. In the worst case, communities may even be disconnected, especially when running the algorithm iteratively. In our experimental analysis, we observe that up to 25% of the communities are badly connected and up to 16% are disconnected. To address this problem, we introduce the Leiden algorithm. We prove that the Leiden algorithm yields communities that are guaranteed to be connected. In addition, we prove that, when the Leiden al
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