Solution

ID: past-exam-of-the-options-ii-course-of-the-university-of-oxford/2011/m/m5/b/ii/solution

Let and define
The probabilities sum to . For , the incoming probability is
using a telescoping sum. Similarly,
Thus is a stationary distribution. Every state can reach in one step, and can reach every lower positive state in one step, so the chain is irreducible. The self-loop at has probability , hence the chain is aperiodic. The convergence theorem for a finite irreducible aperiodic Markov chain now gives
For , the conclusion follows directly from the single absorbing/refilled state.
This is the limiting law of the uniform depletion and refill Markov chain.

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