Critical Slowing Down of Cluster Algorithms for Ising Models Coupled to 2-d Gravity
Mark J. Bowick, Marco Falcioni, Geoffrey Harris, Enzo Marinari
Abstract
We simulate single and multiple Ising models coupled to 2–d gravity using both the Swendsen-Wang and Wolff algorithms to update the spins. We study the integrated autocorrelation time and find that there is considerable critical slowing down, particularly in the magnetization. We argue that this is primarily due to the local nature of the dynamical triangulation algorithm and to the generation of a distribution of baby universes which inhibits cluster growth. SU–HEP–93–4241–560 SCCS 568 hep-lat/9311036 Considerable work has been devoted to the study of the performance of cluster algorithms in reducing the critical slowing down of many statistical models. The Swendsen-Wang [1] and the Wolff [2] algorithms have proven very effective in beating the critical slowing down (CSD) exhibited by these models when simulated with a standard Metropolis [3] update. Reviews on cluster algorithms and CSD may be found on refs. [4]. In recent years, the numerical study of Potts models coupled to 2–d gravity has received much attention [5, 6, 7], aided as well by increased analytical understanding of these models [8]. Cluster algorithms have proved useful in saving computational effort on the update of the Potts variables. The present study is motivated by the fact that there is little understanding of the actual extent of the improvement achieved in these simulations. It is worthwhile, therefore, to measure CSD in the case of simple Ising spins coupled to a dynamical lattice in order to quantify the performance of cluster algorithms. We find that there is considerable CSD, especially in the magnetization, and we relate this to the dynamics of cluster formation on a random lattice.