Publicació: |
Centre de Recerca Matemàtica 2011 |
Descripció: |
20 p. |
Resum: |
In a seminal paper [10], Weitz gave a deterministic fully polynomial approximation scheme for counting exponentially weighted independent sets (which is the same as approximating the partition function of the hard-core model from statistical physics) in graphs of degree at most d, up to the critical activity for the uniqueness of the Gibbs measure on the in nite d-regular tree. More recently Sly [8] (see also [1]) showed that this is optimal in the sense that if there is an FPRAS for the hard-core partition function on graphs of maximum degree d for activities larger than the critical activity on the in nite d-regular tree then NP = RP. In this paper we extend Weitz's approach to derive a deterministic fully polynomial approximation scheme for the partition function of general two-state anti-ferromagnetic spin systems on graphs of maximum degree d, up to the corresponding critical point on the d-regular tree. The main ingredient of our result is a proof that for two-state anti-ferromagnetic spin systems on the d-regular tree, weak spatial mixing implies strong spatial mixing. This in turn uses a message-decay argument which extends a similar approach proposed recently for the hard-core model by Restrepo et al [7] to the case of general two-state anti-ferromagnetic spin systems. |
Drets: |
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Llengua: |
Anglès |
Col·lecció: |
Centre de Recerca Matemàtica. Prepublicacions |
Col·lecció: |
Prepublicacions del Centre de Recerca Matemàtica ; 1038 |
Document: |
Article ; Prepublicació ; Versió de l'autor |
Matèria: |
Aproximació, Teoria de l' ;
Algorismes |