Testing ±1-weight halfspace

  • Authors:
  • Kevin Matulef;Ryan O'Donnell;Ronitt Rubinfeld;Rocco A. Servedio

  • Affiliations:
  • MIT,;Carnegie Mellon University,;Tel Aviv University and MIT,;Columbia University,

  • Venue:
  • APPROX '09 / RANDOM '09 Proceedings of the 12th International Workshop and 13th International Workshop on Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques
  • Year:
  • 2009

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Abstract

We consider the problem of testing whether a Boolean function f :{ - 1,1} n --{ - 1,1} is a ±1-weight halfspace , i.e. a function of the form f (x ) = sgn(w 1 x 1 + w 2 x 2 + ... + w n x n ) where the weights w i take values in { - 1,1}. We show that the complexity of this problem is markedly different from the problem of testing whether f is a general halfspace with arbitrary weights. While the latter can be done with a number of queries that is independent of n [7], to distinguish whether f is a ±-weight halfspace versus ε -far from all such halfspaces we prove that nonadaptive algorithms must make Ω(logn ) queries. We complement this lower bound with a sublinear upper bound showing that $O(\sqrt{n}\cdot $poly$(\frac{1}{\epsilon}))$ queries suffice.