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Exit Frequency Matrices for Finite Markov Chains

Published online by Cambridge University Press:  14 May 2010

ANDREW BEVERIDGE
Affiliation:
Department of Mathematics and Computer Science, Macalester College, Saint Paul, MN 55105, USA (e-mail: abeverid@macalester.edu)
LÁSZLÓ LOVÁSZ
Affiliation:
Institute of Mathematics, Eötvös Loránd University, Budapest, Hungary (e-mail: lovasz@cs.elte.hu)
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Abstract

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Consider a finite irreducible Markov chain on state space S with transition matrix M and stationary distribution π. Let R be the diagonal matrix of return times, Rii = 1/πi. Given distributions σ, τ and kS, the exit frequency xk(σ, τ) denotes the expected number of times a random walk exits state k before an optimal stopping rule from σ to τ halts the walk. For a target distribution τ, we define Xτ as the n × n matrix given by (Xτ)ij = xj(i, τ), where i also denotes the singleton distribution on state i.

The dual Markov chain with transition matrix = RMR−1 is called the reverse chain. We prove that Markov chain duality extends to matrices of exit frequencies. Specifically, for each target distribution τ, we associate a unique dual distribution τ*. Let denote the matrix of exit frequencies from singletons to τ* on the reverse chain. We show that , where b is a non-negative constant vector (depending on τ). We explore this exit frequency duality and further illuminate the relationship between stopping rules on the original chain and reverse chain.

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Copyright © Cambridge University Press 2010