Approximating the partition function of the ferromagnetic Potts model

  • Authors:
  • Leslie Ann Goldberg;Mark Jerrum

  • Affiliations:
  • Department of Computer Science, University of Liverpool, Liverpool, United Kingdom;School of Mathematical Sciences, Queen Mary, University of London, London, United Kingdom

  • Venue:
  • ICALP'10 Proceedings of the 37th international colloquium conference on Automata, languages and programming
  • Year:
  • 2010

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Abstract

We provide evidence that it is computationally difficult to approximate the partition function of the ferromagnetic q-state Potts model when q 2. Specifically we show that the partition function is hard for the complexity class #RHΠ1 under approximation-preserving reducibility. Thus, it is as hard to approximate the partition function as it is to find approximate solutions to a wide range of counting problems, including that of determining the number of independent sets in a bipartite graph. Our proof exploits the first order phase transition of the "random cluster" model, which is a probability distribution on graphs that is closely related to the q-state Potts model. A full version of this paper, with proofs included, is available at http://arxiv.org/abs/1002.0986.