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arXiv 0810.2777math.PRmath.SP
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再论马尔可夫链的Harris遍历定理

Yet another look at Harris' ergodic theorem for Markov chains

Martin Hairer, Jonathan C. Mattingly

摘要:

本文给出了马尔可夫链的Harris遍历定理的一个变形的初等证明。这个定理,可以追溯到50年代,基本上说,一个马尔可夫链是唯一遍历,如果它允许一个“小”集,这是访问无限频繁。这给出了一个扩展的想法Doeblin的无界状态空间设置。通常这是通过找到一个具有“小”水平集的李雅普诺夫函数来建立的。这个问题已经研究了许多作者(cf. Harris,Hasminskii,Nummelin,Meyn and Tweedie).如果李雅普诺夫函数足够强,则在加权上确界范数中存在谱间隙(参见图1)。Meyn和Tweedie)。传统的证明这一结果依赖于分解的马尔可夫链到远足远离小集和仔细分析的指数尾的长度,这些远足。还有其他的变体,它们利用了泊松方程,或致力于得到显式常数。本证明是非常直接的,而是依赖于引入一个家庭的等价加权范数索引的参数$β$,并作出适当的选择,这个参数,允许结合在一个非常基本的方式的两个成分(存在的李雅普诺夫函数和不可约),这是至关重要的,在获得一个频谱间隙。这个证明的最初动机是作者对Wasserstein度量中的谱隙的研究。本说明中的证明是我们在全变差设置中推理的一个版本,我们使用该设置来指导arXiv:math/0602479中的计算。虽然我们最初是为此目的编写这份报告的,但我们希望它本身将引起人们的兴趣。

英文摘要:

The aim of this note is to present an elementary proof of a variation of Harris' ergodic theorem of Markov chains. This theorem, dating back to the fifties essentially states that a Markov chain is uniquely ergodic if it admits a ``small'' set which is visited infinitely often. This gives an extension of the ideas of Doeblin to the unbounded state space setting. Often this is established by finding a Lyapunov function with ``small'' level sets. This topic has been studied by many authors (cf. Harris, Hasminskii, Nummelin, Meyn and Tweedie). If the Lyapunov function is strong enough, one has a spectral gap in a weighted supremum norm (cf. Meyn and Tweedie). Traditional proofs of this result rely on the decomposition of the Markov chain into excursions away from the small set and a careful analysis of the exponential tail of the length of these excursions. There have been other variations which have made use of Poisson equations or worked at getting explicit constants. The present proof is very direct, and relies instead on introducing a family of equivalent weighted norms indexed by a parameter $β$ and to make an appropriate choice of this parameter that allows to combine in a very elementary way the two ingredients (existence of a Lyapunov function and irreducibility) that are crucial in obtaining a spectral gap. The original motivation of this proof was the authors' work on spectral gaps in Wasserstein metrics. The proof presented in this note is a version of our reasoning in the total variation setting which we used to guide the calculations in arXiv:math/0602479. While we initially produced it for that purpose, we hope that it will be of interest in its own right.

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