On the noise sensitivity of monotone functions

  • Authors:
  • Elchanan Mossel;Ryan O'Donnell

  • Affiliations:
  • Statistics, University of California, Berkeley, California;Mathematics Department, Massachusetts Institute of Technology, Cambridge, Massachusetts

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

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Abstract

It is known that for all monotone functions f : {0, 1}n → {0, 1}, if x ∈ {0, 1}n is chosen uniformly at random and y is obtained from x by flipping each of the bits of x independently with probability ε = n-α then P[f(x) ≠ f(y)] -α+1/2, for some c P[fn(x) ≠ fn(y)] ≥ δ, where 0 c(δ)n-α, where α = 1 - ln 2/ln 3 = 0.36907..., and c(δ) 0. We improve this result by achieving for every 0 P[fn(x) ≠ fn(y)] ≥ δ, with: • ε = c(δ)n-α for any α k = k(α); • ε = c(δ)n-1/2logtn for t = log2√π/2 = .3257 ..., using an explicit recursive majority function with increasing arities; and • ε = c(δ)n-1/2, nonconstructively, following a probabilistic CNF construction due to Talagrand.We also study the problem of achieving the best dependence on δ in the case that the noise rate ε is at least a small constant; the results we obtain are tight to within logarithmic factors.