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Computational Transition at the Uniqueness Threshold

2010/05/31 by Sly, Allan · 5 citations
#Computational Complexity (cs.CC) #FOS: Computer and information sciences #FOS: Mathematics #FOS: Physical sciences #Mathematical Physics (math-ph) #Probability (math.PR)

paper · doi:10.48550/arxiv.1005.5584

Abstract

The hardcore model is a model of lattice gas systems which has received much attention in statistical physics, probability theory and theoretical computer science. It is the probability distribution over independent sets I of a graph weighted proportionally to λ|I| with fugacity parameter λ. We prove that at the uniqueness threshold of the hardcore model on the d-regular tree, approximating the partition function becomes computationally hard on graphs of maximum degree d. Specifically, we show that unless NP=RP there is no polynomial time approximation scheme for the partition function (the sum of such weighted independent sets) on graphs of maximum degree d for fugacity λc(d) < λ< λc(d) + ε(d) where λc = \frac(d-1)d-1(d-2)d is the uniqueness threshold on the d-regular tree and ε(d)>0. Weitz produced an FPTAS for approximating the partition function when 0

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