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Miquel Oliu-Barton

Publications and source records attributed to Miquel Oliu-Barton.

13 recordsLinked to original sources
arXiv2023

Absorbing games with irrational values

Can an absorbing game with rational data have an irrational limit value? Yes: In this note we provide the simplest examples where this phenomenon arises. That is, the following $3\times 3$ absorbing game \[ A = \begin{bmatrix} 1^* & 1^* & 2^* \\ 1^* & 2^* & 0\phantom{^*} \\ 2^* & 0\phantom{^*} & 1^* \end{bmatrix}, \] and a sequence of $2\times 2$ absorbing games whose limit values are $\sqrt{k}$, for all integer $k$. Finally, we conjecture that any algebraic number can be represented as the limit value of an absorbing game.

math.OC↗
arXiv2022

Constant payoff in zero-sum stochastic games

In a zero-sum stochastic game, at each stage, two adversary players take decisions and receive a stage payoff determined by them and by a controlled random variable representing the state of nature. The total payoff is the normalized discounted sum of the stage payoffs. In this paper we solve the "constant payoff" conjecture formulated by Sorin, Vigeral and Venel (2010): if both players use optimal strategies, then for any alpha>0, the expected discounted payoff between stage 1 and stage alpha/lambda tends to the limit discounted value of the game, as the discount rate lambda goes to 0.

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arXiv2021

Optimal strategies in repeated games with incomplete information: the dependent case

Using the duality techniques introduced by De Meyer (1996a, 1996b), De Meyer and Marino (2005) provided optimal strategies for both players in finitely repeated games with incomplete information on two sides, in the independent case. In this note, we extend both the duality techniques and the construction of optimal strategies to the case of general type dependence.

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arXiv2020

Occupation measures arising in finite stochastic games

Shapley (1953) introduced two-player zero-sum discounted stochastic games, henceforth stochastic games, a model where a state variable follows a two-controlled Markov chain, the players receive rewards at each stage which add up to $0$, and each maximizes the normalized $\la$-discounted sum of stage rewards, for some fixed discount rate $\la\in(0,1]$. In this paper, we study asymptotic occupation measures arising in these games, as the discount rate goes to $0$.

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arXiv2020

Constant payoff in absorbing games

In this paper, we solve the constant-payoff conjecture formulated by Sorin, Venel and Vigeral (2010), for absorbing games with an arbitrary evaluation of the stage rewards. That is, the existence of a pair of asymptotically optimal strategies, indexed by the evaluation of the stage rewards, so that the average rewards are constant on any fraction of the game. That the constant-payoff conjecture holds for stochastic games with an arbitrary evaluation is still open.

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arXiv2019

A formula for the value of a stochastic game

In 1953, Lloyd Shapley defined the model of stochastic games, which were the first general dynamic model of a game to be defined, and proved that competitive stochastic games have a discounted value. In 1982, Jean-François Mertens and Abraham Neyman proved that competitive stochastic games admit a robust solution concept, the value, which is equal to the limit of the discounted values as the discount rate goes to 0. Both contributions were published in PNAS. In the present paper, we provide a tractable formula for the value of competitive stochastic games.

math.PR↗
arXiv2019

New algorithms for solving stochastic games

Stochastic games are a classical model in game theory in which two opponents interact and the environment changes in response to the players' behavior. The central solution concepts for these games are the discounted values and the value, which represent what playing the game is worth to the players for different levels of impatience. In the present manuscript, we provide algorithms for computing exact expressions for the discounted values and for the value, which are polynomial in the number of pure stationary strategies of the players. This result considerably improves all the existing algorithms, including the most efficient one, due to Hansen, Koucký, Lauritzen, Miltersen and Tsigaridas (STOC 2011).

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arXiv2014

Differential games with asymmetric and correlated information

Differential games with asymmetric information were introduced by Cardaliaguet (2007). As in repeated games with lack of information on both sides (Aumann and Maschler (1995)), each player receives a private signal (his type) before the game starts and has a prior belief about his opponent's type. Then, a differential game is played in which the dynamic and the payoff function depend on both types: each player is thus partially informed about the differential game that is played. The existence of the value function and some characterizations have been obtained under the assumption that the signals are drawn independently. In this paper, we drop this assumption and extend these two results to the general case of correlated types. This result is then applied to repeated games with incomplete information: the characterization of the asymptotic value obtained by Rosenberg and Sorin (2001) and Laraki (2001) for the independent case is extended to the general case.

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arXiv2013

A strategy-based proof of the existence of the value in zero-sum differential games

The value of a zero-sum differential games is known to exist, under Isaacs' condition, as the unique viscosity solution of a Hamilton-Jacobi-Bellman equation. In this note we provide a self-contained proof based on the construction of $\ep$-optimal strategies, which is inspired by the "extremal aiming" method from Krasovskii and Subbotin.

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arXiv2013

Existence of the uniform value in repeated games with a more informed controller

We prove that in a general zero-sum repeated game where the first player is more informed than the second player and controls the evolution of information on the state, the uniform value exists. This result extends previous results on Markov decision processes with partial observation (Rosenberg, Solan, Vieille 2002), and repeated games with an informed controller (Renault 2012). Our formal definition of a more informed player is more general than the inclusion of signals, allowing therefore for imperfect monitoring of actions. We construct an auxiliary stochastic game whose state space is the set of second order beliefs of player 2 (beliefs about beliefs of player 1 on the true state variable of the initial game) with perfect monitoring and we prove it has a value by using a result of Renault 2012. A key element in this work is to prove that player 1 can use strategies of the auxiliary game in the initial game in our general framework, which allows to deduce that the value of the auxiliary game is also the value of our initial repeated game by using classical arguments.

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arXiv2010

A uniform Tauberian theorem in optimal control

In an optimal control framework, we consider the value $V_T(x)$ of the problem starting from state $x$ with finite horizon $T$, as well as the value $V_λ(x)$ of the $λ$-discounted problem starting from $x$. We prove that uniform convergence (on the set of states) of the values $V_T(\cdot)$ as $T$ tends to infinity is equivalent to uniform convergence of the values $V_λ(\cdot)$ as $λ$ tends to 0, and that the limits are identical. An example is also provided to show that the result does not hold for pointwise convergence. This work is an extension, using similar techniques, of a related result in a discrete-time framework \cite{LehSys}.

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