Almost-Euclidean subspaces of l1Nvia tensor products: a simple approach to randomness reduction

  • Authors:
  • Piotr Indyk;Stanislaw Szarek

  • Affiliations:
  • MIT;CWRU & Paris 6

  • Venue:
  • APPROX/RANDOM'10 Proceedings of the 13th international conference on Approximation, and 14 the International conference on Randomization, and combinatorial optimization: algorithms and techniques
  • Year:
  • 2010

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Abstract

It has been known since 1970's that the N-dimensional l1- space contains almost Euclidean subspaces whose dimension is Ω(N). However, proofs of existence of such subspaces were probabilistic, hence non-constructive, which made the results not-quite-suitable for subsequently discovered applications to high-dimensional nearest neighbor search, error-correcting codes over the reals, compressive sensing and other computational problems. In this paper we present a "low-tech" scheme which, for any γ 0, allows us to exhibit almost Euclidean Ω(N)- dimensional subspaces of l1N while using only Nγ random bits. Our results extend and complement (particularly) recent work by Guruswami-Lee-Wigderson. Characteristic features of our approach include (1) simplicity (we use only tensor products) and (2) yielding almost Euclidean subspaces with arbitrarily small distortions.