Slow Mixing of Markov Chains Using Fault Lines and Fat Contours

  • Authors:
  • Sam Greenberg;Dana Randall

  • Affiliations:
  • School of Mathematics, Georgia Institute of Technology, Atlanta, GA 30332-0160,;College of Computing, Georgia Institute of Technology, Atlanta, GA 30332-0280,

  • Venue:
  • APPROX '07/RANDOM '07 Proceedings of the 10th International Workshop on Approximation and the 11th International Workshop on Randomization, and Combinatorial Optimization. Algorithms and Techniques
  • Year:
  • 2007

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Abstract

We show that local dynamics require exponential time for two sampling problems: independent sets on the triangular lattice (the hard-core lattice gas model) and weighted even orientations of the Cartesian lattice (the 8-vertex model). For each problem, there is a parameter 茂戮驴known as the fugacity such that local Markov chains are expected to be fast when 茂戮驴is small and slow when 茂戮驴is large. However, establishing slow mixing for these models has been a challenge because standard contour arguments typically used to show that a chain has small conductance do not seem sufficient. We modify this approach by introducing the notion of fat contoursthat can have nontrivial d-dimensional volume and use these to establish slow mixing of local chains defined for these models.