Probabilistic community detection with unknown number of communities

A fundamental problem in network analysis is clustering the nodes into groups, each of which shares a similar connectivity pattern. Existing algorithms for community detection assume the knowledge of the number of clusters or estimate it a priori using various selection criteria and subsequently estimate the community structure. Ignoring the uncertainty in the first stage may lead to erroneous clustering, particularly when the community structure is vague. We instead propose a coherent probabilistic framework (MFM-SBM) for simultaneous estimation of the number of communities and the community structure, adapting recently developed Bayesian nonparametric techniques to network models. An efficient Markov chain Monte Carlo (MCMC) algorithm is proposed which obviates the need to perform reversible jump MCMC on the number of clusters. The methodology is shown to outperform recently developed community detection algorithms in a variety of synthetic data examples and in benchmark real-datasets. We derive non-asymptotic bounds on the marginal posterior probability of the true configuration, and subsequently use it to prove a clustering consistency result which is novel in the Bayesian context to best of our knowledge.