Deterministic construction of a high dimensional lp section in l1n for any p

  • Authors:
  • Zohar S. Karnin

  • Affiliations:
  • Technion, Israel Institute of Technology, Haifa, Israel

  • Venue:
  • Proceedings of the forty-third annual ACM symposium on Theory of computing
  • Year:
  • 2011

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Abstract

For any 00, we give an efficient deterministic construction of a linear subspace V ⊆ Rn, of dimension (1-ε)n in which the lp and lr norms are the same up to a multiplicative factor of poly(ε-1) (after proper normalization). As a corollary we get a deterministic compressed sensing algorithm (Basis Pursuit) for a new range of parameters. In particular, for any constant ε0 and pn - Rε n with the l1/lp guarantee for (n ⋅ poly(ε))-sparse vectors. Namely, let x be a vector in Rn whose l1 distance from a k-sparse vector (for some k=n ⋅ poly(ε)) is δ. The algorithm, given Ax as input, outputs an n dimensional vector y such that ||x-y||p ≤ δ k1/p-1. In particular this gives a weak form of the l2/l1 guarantee. Our construction has the additional benefit that when viewed as a matrix, A has at most O(1) non-zero entries in each row. As a result, both the encoding (computing Ax) and decoding (retrieving x from Ax) can be computed efficiently.