Welcome

The Séminaire parisien de Théorie des Jeux is an open, inter-institutional, multi-disciplined seminar which covers all fields of game theory. It takes place on Monday from 11:00 to 12:00 am at Institut Henri Poincaré, 11 rue Pierre et Marie Curie, Paris 5ème.

Unless otherwise specified, the seminar is in presence.

You will find the program for the current academic year on the page 2023/2024 and the program for past years on the page Archives.

The junior seminar welcomes PhD students in game theory to present their work.  You will find the program for the current academic year on the page Junior Seminar 2023/2024.

Next seminar:

May 27, 2024 ,10:00-12:00, room Maryam Mirzakhani (201):

11:00-12:00 : Julien GRAND-CLEMENT  (HEC) On the connection between stochastic games and robust optimization, with Nicolas Vieille (HEC Paris) and Marek Petrik (University of New Hampshire).

Abstract: Robust Markov Decision Processes (RMDPs) are a widely used framework for sequential decision-making under parameter uncertainty. RMDPs have been extensively studied when the objective is to maximize the discounted return, but little is known for average optimality (optimizing the long-run average of the rewards obtained over time) and Blackwell optimality (remaining discount optimal for all discount factors sufficiently close to 1). In this paper, we prove several foundational results for RMDPs beyond the discounted return. We show that average optimal policies can be chosen stationary and deterministic for sa-rectangular RMDPs but, perhaps surprisingly, that history-dependent (Markovian) policies strictly outperform stationary policies for average optimality in s-rectangular RMDPs. We also study Blackwell optimality for sa-rectangular RMDPs, where we show that approximate Blackwell optimal policies always exist, although Blackwell optimal policies may not exist. We also provide a sufficient condition for their existence, which encompasses virtually any examples from the literature. We then discuss the connection between average and Blackwell optimality, and we describe several algorithms to compute the optimal average return. Interestingly, our approach leverages the connections between RMDPs and stochastic games.

10:00-11:00: Dimitrios XEFTERIS  (University of Cyprus) Information Aggregation with Delegation of Votes, with Amrita Dhillon (King’s College London), Grammateia Kotsialou (London School of Economics), Dilip Ravindran (Humboldt University of Berlin), Dimitrios Xefteris (University of Cyprus)

Abstract: Liquid democracy is a system that combines  aspects of direct democracy and representative democracy by allowing voters to either vote directly themselves, or delegate their votes to others. In this paper we study the information aggregation properties of liquid democracy in a setting with heterogeneously informed truth-seeking voters who want the election outcome to match an underlying state of the world and partisan voters. We establish that liquid democracy admits equilibria which improve welfare and information aggregation over direct and representative democracy when voters' preferences and information precisions are publicly or privately known. When precisions are commonly known, we provide sufficient conditions for this improvement being strict and characterize optimal delegation for important classes of committees. Liquid democracy also admits equilibria which do worse than the other two systems. We discuss features of efficient and inefficient equilibria and provide conditions under which voters can more easily coordinate on the efficient equilibria in liquid democracy than the other two systems.

Organizers

Frédéric Koessler (CNRS, GREGHEC, HEC Paris), frederic.koessler[at]gmail[dot]com

Maël Letreust  (CNRS,  IRISA Rennes), mael.le-treust[at]cnrs[dot]fr

Chantal Marlats (LEMMA, Université Paris Panthéon-Assas), chantal.marlats[at]u-paris2[dot]fr

Yannick Viossat (CEREMADE, PSL), viossat[at]ceremade[dot]dauphine[dot]fr

Bruno Ziliotto (CNRS, CEREMADE, PSL), ziliotto[at]math[dot]cnrs[dot]fr

To join (or unsuscribe from) our mailing list, please contact Chantal Marlats at chantal.marlats[at]u-paris2[dot]fr. 

Former organizers

Joseph Abdou; Bernard De Meyer; Françoise Forges; Olivier Gossner; Fréderic Koessler; Marie Laclau; Rida Laraki; Vianney Perchet; Jérôme Renault; Dinah Rosenberg; Sylvain Sorin; Tristan Tomala; Xavier Venel; Nicolas Vieille; Guillaume Vigeral; Yannick Viossat;