Testing juntas

  • Authors:
  • Eldar Fischer;Guy Kindler;Dana Ron;Shmuel Safra;Alex Samorodnitsky

  • Affiliations:
  • Faculty of Computer Science, Technion-Israel Institute of Technogy, 32000 Haifa, Israel;School of Mathematics Sciences, Tel-Aviv University, Tel-Aviv, Israel;Department of Electrical Engineering, Tel-Aviv University, Tel-Aviv, Israel;School of Mathematics Sciences, Tel-Aviv University, Tel-Aviv, Israel;School of Computer Science and Engineering, The Hebrew University of Jerusalem, Jerusalem, Israel

  • Venue:
  • Journal of Computer and System Sciences - Special issue on FOCS 2002
  • Year:
  • 2004

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Abstract

We show that a boolean valued function over n variables, where each variable ranges in an arbitrary probability space, can be tested for the property of depending on only J of them using a number of queries that depends only polynomially on J and the approximation parameter ε. We present several tests that require a number of queries that is polynomial in J and linear in ε-1. We showa non-adaptive tests that has one-sided error, an adaptive version of it that requires fewer queries, and a non-adaptive two-sided version of the test that requires the least number of queries. We also show a two-sided non-adaptive test that applies to functions over n boolean variables, and has a more compact analysis.We then provide a lower bound of Ω˜(√J) on the number of queries required for the nonadaptive testing of the above property; a lower bound of Ω(log(J + 1)) for adaptive algorithms naturally follows from this. In establishing this lower bound we also prove a result about random walks on the group Z2q that may be interesting in its own right. We show that for some t(q) = Ω˜(q2), the distributions of the random walk at times t and t + 2 are close to each other, independently of the step distribution of the walk.We also discuss related questions. In particular, when given in advance a known J-junta function h, we show how to test a function f for the property of being identical to h up to a permutation of the variables, in a number of queries that is polynomial in J and ε-1.