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# Adaptive Power Method: Eigenvector Estimation from Sampled Data

*Proceedings of The 34th International Conference on Algorithmic Learning Theory*, PMLR 201:1387-1410, 2023.

#### Abstract

Computing the dominant eigenvectors of a matrix $A$ has many applications, such as principal component analysis, spectral embedding, and PageRank. However, in general, this task relies on the complete knowledge of the matrix $A$, which can be too large to store or even infeasible to observe in many applications, e.g., large-scale social networks. Thus, a natural question is how to accurately estimate the eigenvectors of $A$ when only partial observations can be made by sampling entries from $A$. To this end, we propose the Adaptive Power Method (\textsc{APM}), a variant of the well-known power method. At each power iteration, \textsc{APM} adaptively selects a subset of the entries of $A$ to observe based on the current estimate of the top eigenvector. We show that \textsc{APM} can estimate the dominant eigenvector(s) of $A$ with squared error at most $\epsilon$ by observing roughly $O(n\epsilon^{-2} \log^2 (n/\epsilon))$ entries of an $n\times n$ matrix. We present empirical results for the problem of eigenvector centrality computation on two real-world graphs and show that \textsc{APM} significantly outperforms a non-adaptive estimation algorithm using the same number of observations. Furthermore, in the context of eigenvector centrality, \textsc{APM} can also adaptively allocate the observation budget to selectively refine the estimate of nodes with high centrality scores in the graph.