Restricted strong convexity and weighted matrix completion: optimal bounds with noise

  • Authors:
  • Sahand Negahban;Martin J. Wainwright

  • Affiliations:
  • Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA;Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA and Department of Statistics

  • Venue:
  • The Journal of Machine Learning Research
  • Year:
  • 2012

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Abstract

We consider the matrix completion problem under a form of row/column weighted entrywise sampling, including the case of uniformentrywise sampling as a special case. We analyze the associated random observation operator, and prove that with high probability, it satisfies a form of restricted strong convexity with respect to weighted Frobenius norm. Using this property, we obtain as corollaries a number of error bounds on matrix completion in the weighted Frobenius norm under noisy sampling and for both exact and near low-rank matrices. Our results are based on measures of the 'spikiness' and 'low-rankness' of matrices that are less restrictive than the incoherence conditions imposed in previous work. Our technique involves an M-estimator that includes controls on both the rank and spikiness of the solution, and we establish non-asymptotic error bounds in weighted Frobenius norm for recovering matrices lying with lq-"balls" of bounded spikiness. Using information-theoretic methods, we show that no algorithm can achieve better estimates (up to a logarithmic factor) over these same sets, showing that our conditions on matrices and associated rates are essentially optimal.