Grinstead-Snell-Probability · Problem 23

Random Walks

Mathematics · markov-chains-ergodic

Problem

Assume that an ergodic Markov chain has states s1,s2,…,sks_1, s_2, \ldots, s_k. Let Sj(n)S_j^{(n)} denote the number of times that the chain is in state sjs_j in the first nn steps. Let w\mathbf{w} denote the fixed probability row vector for this chain. Show that, regardless of the starting state, the expected value of Sj(n)S_j^{(n)}, divided by nn, tends to wjw_j as n→∞n \to \infty. Hint: If the chain starts in state sis_i, then the expected value of Sj(n)S_j^{(n)} is given by the expression ∑h=0npij(h).\sum_{h=0}^{n} p_{ij}^{(h)}.

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