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Bisimulation Metrics are Optimal Value Functions
Proceedings of the 30th Conference on Uncertainty in Artificial Intelligence, PMLR R12:332-341, 2014.
Abstract
Bisimulation is a notion of behavioural equiva- lence on the states of a transition system. Its defi- nition has been extended to Markov decision pro- cesses, where it can be used to aggregate states. A bisimulation metric is a quantitative analog of bisimulation that measures how similar states are from a the perspective of long-term behavior. Bisimulation metrics have been used to establish approximation bounds for state aggregation and other forms of value function approximation. In this paper, we prove that a bisimulation metric defined on the state space of a Markov decision process is the optimal value function of an opti- mal coupling of two copies of the original model. We prove the result in the general case of con- tinuous state spaces. This result has important implications in understanding the complexity of computing such metrics, and opens up the possi- bility of more efficient computational methods.