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arXiv 0712.0489math.PRmath-phmath.MP
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非顺从图上的Glauber动力学:边界条件和混合时间

Glauber dynamics on nonamenable graphs: Boundary conditions and mixing time

Alessandra Bianchi

摘要:

研究了有限有界度n阶图上的随机Ising模型,分析了边界条件对混合时间的影响。我们证明了对于所有足够低的温度,一类非顺从图上具有(+)-边界条件的动力学的谱间隙在n中是严格一致正的。这意味着混合时间在n中至多线性增长。我们考虑的一类图包括双曲图与足够高的程度,其中的最佳上界的混合时间的自由边界动力学是多项式n,与指数增长的逆温度。此外,我们构造了这类图,对于它,在自由边界情况下的混合时间在n中是指数大的。这提供了第一个例子,其中混合时间在n中从指数跳到线性,同时从自由到(+)-边界条件。这些结果将Martinelli,Sinclair和Weitz的分析推广到更广泛的一类不服从图。

英文摘要:

We study the stochastic Ising model on finite graphs with n vertices and bounded degree and analyze the effect of boundary conditions on the mixing time. We show that for all low enough temperatures, the spectral gap of the dynamics with (+)-boundary condition on a class of nonamenable graphs, is strictly positive uniformly in n. This implies that the mixing time grows at most linearly in n. The class of graphs we consider includes hyperbolic graphs with sufficiently high degree, where the best upper bound on the mixing time of the free boundary dynamics is polynomial in n, with exponent growing with the inverse temperature. In addition, we construct a graph in this class, for which the mixing time in the free boundary case is exponentially large in n. This provides a first example where the mixing time jumps from exponential to linear in n while passing from free to (+)-boundary condition. These results extend the analysis of Martinelli, Sinclair and Weitz to a wider class of nonamenable graphs.

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