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Poster

Exact Community Recovery under Side Information: Optimality of Spectral Algorithms

Julia Gaudio · Nirmit Joshi

Hall 3 + Hall 2B #482
[ ]
Wed 23 Apr 7 p.m. PDT — 9:30 p.m. PDT

Abstract: We study the problem of exact community recovery in general, two-community block models, in the presence of node-attributed *side information*. We allow for a very general side information channel for node attributes, and for pairwise (edge) observations, consider both Bernoulli and Gaussian matrix models, capturing the Stochastic Block Model, Submatrix Localization, and Z2-Synchronization as special cases. A recent work of Dreveton et al. 2024 characterized the information-theoretic limit of a very general exact recovery problem with side information. In this paper, we show algorithmic achievability in the above important cases by designing a simple but optimal spectral algorithm that incorporates side information (when present) along with the eigenvectors of the pairwise observation matrix. Using the powerful tool of entrywise eigenvector analysis [Abbe et al. 2020], we show that our spectral algorithm can mimic the so called *genie-aided estimators*, where the ith genie-aided estimator optimally computes the estimate of the ith label, when all remaining labels are revealed by a genie. This perspective provides a unified understanding of the optimality of spectral algorithms for various exact recovery problems in a recent line of work.

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