MLSE Seminar

Author: Marc Schröder (UM, KE) (joint with Shaul Rosner and Laura Vargas Koch)
Date and time: January 21st, 2025 (13:15-14:15), TS53 A0.24
Title: Nash flows over time with tolls
Abstract: Traffic congestion remains an important problem in our current society. There are multiple ways and approaches to model this. We consider a theoretic, but realistic model known as the deterministic fluid queuing model (or Vickrey's bottleneck model). We introduce (fixed) tolls to the model and test whether some of the known properties of dynamic equilibria carry over. Using three examples we show that (1) dynamic equilibria with tolls need not be unique, (2) particles might overtake in dynamic equilibria with tolls, (3) dynamic equilibria with tolls need not reach a steady state.

Author: Andrés Perea (UM, KE)
Date and time: February 4th, 2025 (13:00-14:00), TS53 A0.23
Title: More reasoning, less outcomes: A monotonicity result for reasoning in dynamic games
Abstract: A focus function in a dynamic game describes, for every player and each of his information sets, the collection of opponents' information sets he reasons about. Every focus function induces a rationalizability procedure in which a player believes, whenever possible, that his opponents choose rationally at those information sets he reasons about. Under certain conditions, I show that if the players start reasoning about more information sets, then the set of outcomes induced by the associated rationalizability procedure becomes smaller or stays the same. This result does not hold on the level of strategies, unless the players only reason about present and future information sets. The monotonicity result enables us to derive existing theorems, such as the relation in terms of outcomes between forward and backward induction reasoning, but also paves the way for new results.

Author: Arnoud den Boer, Jean-Jacques Herings, Philippos Michaelides, Christian Seel (UM, MPE)
Date and time: February 25th, 2025 (13:00-14:00), TS53 A0.23
Title: Algorithmic Learning in Local and Global Public Goods Games.
Abstract: In this paper, we consider two variants of a repeated public goods game. In the global variant, an agent’s reward depends on the contributions of all other agents, whereas in the local variant, introduced by Eshel et al. [1998], an agent’s reward depends only on the contributions of its direct neighbors. We define different solution concepts and derive theoretical predictions for both variants, depending on the altruism cost, the discount factor, and the probability of trembles. We then simulate the interaction between Q-learners under different parameters. We find little convergence to subgame-perfect Nash equilibria and much more convergence to Nash equilibria. Unlike the imitation dynamics in Eshel et al. [1998], Q-learning leads to more altruism in the global variant.

Author: Janos Flesch (UM, KE), Miklós Pintér, Arkadi Predtetchinski (UM, MPE), and William Sudderth
Date and time: March 11th, 2025 (13:15-14:15), TS53 C-1.09
Title: Games with a Finite Yet Arbitrarily Large Number of Active Players
Abstract: We propose a model of games with infinitely many players. Its key feature is that the set of active players is finite almost surely, and yet, every single player becomes active with probability 1. More precisely, in such a game:

1.           A finite set of players, called active, is drawn from an infinite set of potential players, according to the so-called selection charge. The selection charge is a finitely additive probability measure on the collection of finite subsets of players with the property that, for every single player, the probability to be active is 1.

2.           Each active player is informed that she is active, but not of who the other active players are.

3.           Finally, the active players choose their actions simultaneously, and, depending on the set of active players and the action profile, they receive the payoffs.

We examine the Nash equilibria of these games. We show that these games admit a Nash equilibrium under various conditions, among others: (i) when the action sets are compact metric and for each given player, the collection of her payoff functions for the different possible sets of active players is equicontinuous, and (ii) when the players have a common finite action set and each player’s payoff depends on her own action and continuously on the frequency of the actions chosen by the other active players, and (iii) in minority games where there are only two actions and each player’s goal is to choose the action that is chosen by the minority of the active players. Some of these results depend heavily on whether iterated integrals, where one integral is taken with respect to a finitely additive probability measure, depend on the order of integration.

Author: Ákos Miklós Balázs, Péter Biró (Corvinus University of Budapest)
Date and time: March 25th, 2025 (13:00-14:00), TS53 A0.23
Title: Comparing mechanisms for course allocation with contracts
Abstract: We study a course allocation problem with contracts which is unique in several aspects. Courses have lexicographic preferences that favour students from higher priority groups, and within these groups, those students who wish to take the course with higher-priority contract terms. Courses are also characterised by finite capacities. Students have preferences over sets of course-term pairs, which are their private information. However, they can send a signal that contains a ranking over singletons and a capacity for each contract term. It is also restricted that the same course cannot be listed with more than one contract term. We consider six different mechanisms for this course allocation problem: the HBS draft, its slight modification (referred to as SZISZ), the random serial dictatorship (RSD), the deferred acceptance with single (DASTB) and multiple tie break (DAMTB), and the latter followed by the stable improvement cycles algorithm (DAMTB+SIC). Our aim is to compare the performance of these mechanisms from several perspectives. First, we evaluate them by checking whether they satisfy certain desiderata (strategy-proofness, possible and necessary player- and student-efficiency, and pairwise stability). We also show that no mechanism can satisfy both strategy-proofness and pairwise stability, and the same is true for possible student-efficiency and pairwise stability. Next, we use a dataset containing the signalled preferences of students (as well as cardinal utilities) from 2023. We apply each mechanism to these signals several times and calculate some welfare indicators from the resulting matchings. Our findings indicate that although the RSD and DASTB mechanisms satisfy more theoretical desiderata, they are outperformed in most welfare indicators by the SZISZ and even more so by the HBS draft mechanism.

Author: Dries Vermeulen (UM, KE) and Dmitriy Kvasov (Waseda University)
Date and time: April 1st, 2025 (13:00-14:00), TS53 H0.04
Title: Computation of the pre-nucleolus for non-negative monotonic games
Abstract: For a non-negative monotonic game, a coalition is called minimal if every strict subcoalition has a strictly lower value. Each non-negative monotonic game is characterized by its collection W of minimal coalitions, together with the associated value for each minimal coalition.

We show that the collection W* consisting of W, together with all coalitions that consist of a minimal coalition plus exactly one player, determines the pre-nucleolus.

We also identify a subcollection of W* that determines the pre-nucleolus on the set of all non-negative pre-imputations, and that moreover contains only a negligible fraction of all coalitions as the number of players in the game is large.

Author: Yanru Sun (UM, KE), Hao Sun, Panfei Sun, Xuanzhu Jin (UM, KE) and Yimei Yang
Date and time: April 22nd, 2025 (13:00-14:00), TS53 A0.23
Title: Elevating the corporate social responsibility level: A media supervision mechanism based on the Stackelberg-Evolutionary game model
Abstract: Environmental taxes alone may not solve the social dilemma posed by the conflict between the myopic pursuit of profit and the cost of corporate social responsibility (CSR). Designing a reasonable supervision mechanism is crucial to correcting market failures.  We develop a media supervision mechanism through a Stackelberg-Evolutionary game model to study the impact of media supervision on the evolutionary behavior of the manufacturer population. Assuming the media is leader, manufacturers' demands are heterogeneous under different strategy profiles after the media determines the effort level of supervision. The best response of the manufacturer population is the evolutionarily stable strategy under supervision, where the percentage of CSR strategies is defined as CSR level. It is proved that the CSR level elevates with the increase of effort level. We analyze the existence and uniqueness of Stackelberg-Evolutionary equilibrium and a numerical algorithm to compute it. The results show that CSR level under Stackelberg-Evolutionary equilibrium is higher than that without supervision. Our research not only illustrates the effectiveness of media supervision in reducing environmental pollution but also provides suggestions for governments to formulate environmental policies and improve regulatory mechanisms.

Author: Shasha Ding, Bas Dietzenbacher, Hans Peters (UM, KE)
Date and time: May 13th, 2025 (13:15-14:15), TS53 A0.23
Title: Strategic cartel profit sharing
Abstract: This paper studies firms in a collusive oligopoly that divide the cartel profits based on their reported capacities. We model these situations as biform games, where the capacities are strategically reported in the form of threats, and these reported capacities result in a cooperative game. We define a family of allocation rules that divide the cartel profits among the collusive firms based on this cooperative game and study the corresponding equilibrium capacities reported when these allocation rules are implemented. We compare these equilibria with the Cournot equilibrium and particularly focus on the equal split rule, the Shapley value, and the dual equal split rule.

Author: Jing Ren (UM, KE), Iwan Bos (UM, OSE), Dries Vermeulen (UM, KE)
Date and time: May 20th, 2025 (12:00-13:00 ), TS53 C-1.07
Title: Myopic coalition formation
Abstract: This paper studies a dynamic coalition formation process, which generates a myopically rational coalition sequence. Our results show that such a dynamic coalition formation process does not have a cycle, which implies that a myopically rational coalition sequence converges to a stable coalition. Moreover, our results have a wide application in economic and social settings. In this paper, we examine the models with open membership and restricted membership, where the dynamic coalition formation process is acyclic. Additionally, our results apply to the setting with and without ranked admission.

Author: Yang Chen, Bettina Klaus (University of Lausanne), Anh Triêu (UM, KE)
Date and time: June 24th, 2025 (13:00-14:00), TS53 A0.23
Title: Paths to Exclusion Stability in Discrete Allocation Economies
Abstract: We define a blocking dynamics based on Balbuzanov and Kotowski’s (2019) exclusion blocking notion. We apply it to various models of discrete allocation economies, for example, Shapley and Scarf (1974) housing market, housing allocation with existing tenants, and so-called simple economies (Balbuzanov and Kotowski, 2019). We prove that for these economies, there is always a path to exclusion stability from any arbitrary allocation.

Author: Pedro Gonzalez-Fernandez, Stefan Terstiege, and Elias Tsakas (UM, MPE)
Date and time: July 1st, 2025 (14:00-15:00), TS53 C-1.05
Title: Regulating Information
Abstract: Economic agents often seek to acquire information before taking an important action, but in many domains, gathering this information requires approval from a regulator. This paper develops a model in which an agent designs an experiment to inform his decision, but can only implement it if a regulator authorizes it ex ante. We characterize the agent’s optimal experiment under this approval constraint and show that, whenever the regulator rejects full revelation, the agent strategically reduces informativeness in the states where their disagreement is strongest. We then extend the model to settings with multiple regulators, comparing sequential and collective approval mechanisms. The analysis yields predictions for how institutional structure shapes access to information, with applications to clinical trials, data privacy, and ethics boards.