Streaming PCA with many missing entries.
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2015-12-01
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Alternative Title:Matrix completion with column manipulation: near-optimal sample-robustness-rank tradeoffs.
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Abstract:This paper considers the problem of matrix completion when some number of the columns are
completely and arbitrarily corrupted, potentially by a malicious adversary. It is well-known that standard
algorithms for matrix completion can return arbitrarily poor results, if even a single column is corrupted.
One direct application comes from robust collaborative filtering. Here, some number of users are socalled
manipulators who try to skew the predictions of the algorithm by calibrating their inputs to the
system. In this paper, we develop an efficient algorithm for this problem based on a combination of a
trimming procedure and a convex program that minimizes the nuclear norm and the 1,2 norm. Our
theoretical results show that given a vanishing fraction of observed entries, it is nevertheless possible to
complete the underlying matrix even when the number of corrupted columns grows. Significantly, our
results hold without any assumptions on the locations or values of the observed entries of the manipulated
columns. Moreover, we show by an information-theoretic argument that our guarantees are nearly
optimal in terms of the fraction of sampled entries on the authentic columns, the fraction of corrupted
columns, and the rank of the underlying matrix. Our results therefore sharply characterize the tradeoffs
between sample, robustness and rank in matrix completion.
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