Bias Optimality versus Strong 0-Discount Optimality in Markov Control Processes with Unbounded Costs

This paper deals with expected average cost (EAC) and discount-sensitive criteria for discrete-time Markov control processes on Borel spaces, with possibly unbounded costs. Conditions are given under which (a) EAC optimality and strong –1-discount optimality are equivalent; (b) strong 0-discount optimality implies bias optimality; and, conversely, under an additional hypothesis, (c) bias optimality implies strong 0-discount optimality. Thus, in particular, as the class of bias optimal policies is nonempty, (c) gives the existence of a strong 0-discount optimal policy, whereas from (b) and (c) we get conditions for bias optimality and strong 0-discount optimality to be equivalent. A detailed example illustrates our results.