The hardness of approximate optima in lattices, codes, and systems of linear equations

  • Authors:
  • S. Arora;L. Babai;J. Stern;Z. Sweedyk

  • Affiliations:
  • Div. of Comput. Sci., California Univ., Berkeley, CA, USA;-;-;-

  • Venue:
  • SFCS '93 Proceedings of the 1993 IEEE 34th Annual Foundations of Computer Science
  • Year:
  • 1993

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Abstract

We prove the following about the Nearest Lattice Vector Problem (in any l/sub p/ norm), the Nearest Code-word Problem for binary codes, the problem of learning a halfspace in the presence of errors, and some other problems. 1. Approximating the optimum within any constant factor is NP-hard. 2. If for some /spl epsiv/0 there exists a polynomial time algorithm that approximates the optimum within a factor of 2/sup log(0.5-/spl epsiv/)/ /sup n/ then NP is in quasi-polynomial deterministic time: NP/spl sube/DTIME(n/sup poly(log/ /sup n)/). Moreover, we show that result 2 also holds for the Shortest Lattice Vector Problem in the l/sub /spl infin// norm. Improving the factor 2/sup log(0.5-/spl epsiv/)/ /sup n/ to /spl radic/(dim) for either of the lattice problems would imply the hardness of the Shortest Vector Problem in l/sub 2/ norm; an old open problem. Our proofs use reductions from few-prover, one-round interactive proof systems, either directly, or through a set-cover problem.