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Efficient Strategy Iteration for Mean Payoff in Markov Decision Processes

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Automated Technology for Verification and Analysis (ATVA 2017)

Part of the book series: Lecture Notes in Computer Science ((LNPSE,volume 10482))

Abstract

Markov decision processes (MDPs) are standard models for probabilistic systems with non-deterministic behaviours. Mean payoff (or long-run average reward) provides a mathematically elegant formalism to express performance related properties. Strategy iteration is one of the solution techniques applicable in this context. While in many other contexts it is the technique of choice due to advantages over e.g. value iteration, such as precision or possibility of domain-knowledge-aware initialization, it is rarely used for MDPs, since there it scales worse than value iteration. We provide several techniques that speed up strategy iteration by orders of magnitude for many MDPs, eliminating the performance disadvantage while preserving all its advantages.

This work is partially supported by the German Research Foundation (DFG) project “Verified Model Checkers” and the Czech Science Foundation grant No. 15-17564S.

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Notes

  1. 1.

    The usual procedure of achieving this in general is to replace \( Act \) by \(S\times Act \) and adapting \(\mathsf {Av}\), \(\varDelta \), and \(r\) appropriately.

  2. 2.

    Some authors deliberately exclude so called “trivial” or “transient” SCCs, which are single states without a self-loop.

  3. 3.

    The \(\liminf \) is used since the limit may not exist in general for an arbitrary strategy.

  4. 4.

    Note that the procedure found in [34, Sect. 9.2.1] differs from our Algorithm in Line 6. There, the bias is improved over all available actions instead of the gain-optimal ones, which is erroneous. The proofs provided in the corresponding chapter actually prove the correctness of the algorithm as presented here.

  5. 5.

    On crafted models with less than 10 states we observed numerical errors leading to non-convergence and condition numbers of up to \(10^5\).

  6. 6.

    Restricting a general MDP to a MEC results in a “communicating” MDP.

  7. 7.

    We will go into detail why we do not deal with bias later on.

  8. 8.

    Accessible at https://www7.in.tum.de/~meggendo/artifacts/2017/atva_si.txt.

  9. 9.

    http://ojalgo.org/.

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Acknowledgments

We thank the anonymous reviewers for their insightful comments and valuable suggestions. In particular, a considerable improvement to the BSCC compression approach of Sect. 4.2 has been proposed.

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Correspondence to Tobias Meggendorfer .

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Křetínský, J., Meggendorfer, T. (2017). Efficient Strategy Iteration for Mean Payoff in Markov Decision Processes. In: D'Souza, D., Narayan Kumar, K. (eds) Automated Technology for Verification and Analysis. ATVA 2017. Lecture Notes in Computer Science(), vol 10482. Springer, Cham. https://doi.org/10.1007/978-3-319-68167-2_25

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