# The period of a state is the greatest common divisor

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Unformatted text preview: 1 ⇢xy ⇢yy so y is recurrent if and only if Ey N (y ) = 1. Theorems 1.5 and 1.7 allow us to decompose the state space and simplify the study of Markov chains. Theorem 1.8. If the state space S is ﬁnite, then S can be written as a disjoint union T [ R1 [ · · · [ Rk , where T is a set of transient states and the Ri , 1 i k , are closed irreducible sets of recurrent states. Stationary distributions A stationary measure is a nonnegative solution of µp = µ A stationary distribution is a nonnegative solution of ⇡ p = ⇡ normalized so that the entries sum to 1. The ﬁrst question is: do these things exist? Theorem 1.20. Suppose p is irreducible and recurrent. Let x 2 S and let Tx = inf {n 1 : Xn = x}. µx (y ) = 1 X Px (Xn = y, Tx &gt; n) n=0 deﬁnes a stationary measure with 0 &lt; µx (y ) &lt; 1 for all y . 61 1.11. CHAPTER SUMMARY If the state space S is ﬁnite and irreducible there is a unique stationary distribution. More generally if Ex Tx &lt; 1, i.e., x is positive recurrent then µ...
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## This document was uploaded on 03/06/2014 for the course MATH 4740 at Cornell University (Engineering School).

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