On restricted min-wise independence of permutations

  • Authors:
  • Jiř/í/ Matouš/ek;Miloš/ Stojaković/

  • Affiliations:
  • Department of Applied Mathematics and Institute of Theoretical Computer Science (ITI), Charles University, Malostranské/ ná/m. 25, 118 00 Praha 1, Czech Republic and Institut fü/r Theo ...;Institut fü/r Theoretische Informatik, ETH Zentrum, Zü/rich, Switzerland/ Institute of Mathematics, University of Novi Sad, Trg D. Obradovic´/a 4, 21000 Novi Sad, Yugoslavia

  • Venue:
  • Random Structures & Algorithms
  • Year:
  • 2003

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Abstract

A family of permutations F ⊆ Sn, with a probability distribution on it is called k-restricted rain-wise independent if we have Pr[min π(X) = π(x)] = 1|X| for every subset X ⊆ [n] with |X| ≤ k, every x ∈ X, and π ∈ F chosen at random. We present a simple proof of a result of Norin: every such family has size at least (n-1 k-1/2) . Some features of our method might be of independent interest. The best available upper bound for the size of such family is 1 + σj=2k(J - 1) (n j). We show that this bound is tight if the goal is to imitate not the uniform distribution on Sn, but a distribution given by assigning suitable priorities to the elements of [n] (the stationary distribution of the Tsetlin library, or self-organizing lists). This is analogous to a result of Karloff and Mansour for k-wise independent random variables. We also investigate the cases where the min-wise independence condition is required only for sets X of size exactly k (where we have only an ω(log log n + k) lower bound), or for sets of size k and k - 1 (where we already obtain a lower bound of n - k + 2).