Gaussian Bounds for Noise Correlation of Functions and Tight Analysis of Long Codes

  • Authors:
  • Elchanan Mossel

  • Affiliations:
  • -

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

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Abstract

We derive tight bounds on the expected value ofproducts of low influencefunctions defined on correlated probability spaces.The proofs are based on extending Fourier theory to an arbitrary number of correlatedprobability spaces, on a generalization of an invariance principlerecently obtained with O'Donnell andOleszkiewicz for multilinear polynomials withlow influences and bounded degree and on properties of multi-dimensionalGaussian distributions.Let $(X_i^j : 1 \leq i \leq k, 1 \leq j \leq n)$ be a matrix of random variables whose columns $X^1,\ldots,X^n$ are independent and identically distributed and such that any two rows $X_i, X_j$ for $1\leq i \neq j \leq k$ are independent.Assume further that the values that row $X_i$ takes with non-zero probability are the same no matter how one conditions on the remaining rows $X_1,\ldots,X_{i-1},X_{i+1},\ldots,X_k$.Our results show that given $k$ functions $f_1,\ldots,f_k$ taking values in $[0,1]$ it holds that $|\E[\prod_{i=1}^k f_i(X_i)] - \prod_{i=1}^k \E[f_i(X_i)]