Locally Testing Direct Product in the Low Error Range

  • Authors:
  • Irit Dinur;Elazar Goldenberg

  • Affiliations:
  • -;-

  • Venue:
  • FOCS '08 Proceedings of the 2008 49th Annual IEEE Symposium on Foundations of Computer Science
  • Year:
  • 2008

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Abstract

Given a function f : X -{0,1}, its `ell’ wise direct productis the function F = f`ell : X^ell - {0,1}^ell defined by:F(x_1,...,x_ell)= (f(x_1),..,f(x_ell)).: We are interestedin the local testability of the direct product encoding(mapping f- f^ell). Namely, given an arbitrary functionF : X^ell-{0,1}^ell, we wish to determine how close itis to f`ell for some f : X-{0,1}, by making two randomqueries into F. In this work we analyze the case of lowacceptance probability of the test. We show that even ifthe test passes with small probability, epsilon 0, already Fmust have a non-trivial structure and in particular mustagree with some f^ell on nearly epsilon of the domain. Moreover,we give a structural characterization of all functions Fon which the test passes with probability epsilon.Our results can be viewed as a combinatorial analogof the low error ‘low degree test’, that is used in PCPconstructions.