scholarly journals Implementation of Subgame-Perfect Cooperative Agreement in an Extensive-Form Game

2021 ◽  
Vol 14 ◽  
pp. 257-272
Author(s):  
Denis Kuzyutin ◽  
◽  
Yulia Skorodumova ◽  
Nadezhda Smirnova ◽  
◽  
...  
Keyword(s):  
Fishery Management ◽  
Solution Concept ◽  
Extensive Form ◽  
Game Tree ◽  
Extensive Form Games ◽  
Payoff Distribution ◽  
Novel Approach ◽  
Cooperation Incentives ◽  
Subgame Perfection ◽  
The Difference

A novel approach to sustainable cooperation called subgameperfect core (S-P Core) was introduced by P. Chander and M. Wooders in 2020 for n-person extensive-form games with terminal payoffs. This solution concept incorporates both subgame perfection and cooperation incentives and implies certain distribution of the total players' payoff at the terminal node of the cooperative history. We use in the paper an extension of the S-P Core to the class of extensive games with payoffs defined at all nodes of the game tree that is based on designing an appropriate payoff distribution procedure β and its implementation when a game unfolds along the cooperative history. The difference is that in accordance with this so-called β-subgameperfect core the players can redistribute total current payoff at each node in the cooperative path. Moreover, a payoff distribution procedure from the β-S-P Core satisfies a number of good properties such as subgame efficiency, non-negativity and strict balance condition. In the paper, we examine different properties of the β-S-P Core, introduce several refinements of this cooperative solution and provide examples of its implementation in extensive-form games. Finally, we consider an application of the β-S-P Core to the symmetric discrete-time alternating-move model of fishery management.

scholarly journals Solving Large Extensive-Form Games with Strategy Constraints

2019 ◽  
Vol 33 ◽  
pp. 1861-1868
Author(s):  
Trevor Davis ◽  
Kevin Waugh ◽  
Michael Bowling
Keyword(s):  
Private Information ◽  
Imperfect Information ◽  
Risk Mitigation ◽  
Solution Concept ◽  
Optimal Strategies ◽  
Linear Constraints ◽  
Convex Constraints ◽  
Extensive Form ◽  
Extensive Form Games ◽  
Large Extensive Form Games

Extensive-form games are a common model for multiagent interactions with imperfect information. In two-player zerosum games, the typical solution concept is a Nash equilibrium over the unconstrained strategy set for each player. In many situations, however, we would like to constrain the set of possible strategies. For example, constraints are a natural way to model limited resources, risk mitigation, safety, consistency with past observations of behavior, or other secondary objectives for an agent. In small games, optimal strategies under linear constraints can be found by solving a linear program; however, state-of-the-art algorithms for solving large games cannot handle general constraints. In this work we introduce a generalized form of Counterfactual Regret Minimization that provably finds optimal strategies under any feasible set of convex constraints. We demonstrate the effectiveness of our algorithm for finding strategies that mitigate risk in security games, and for opponent modeling in poker games when given only partial observations of private information.

scholarly journals Smoothing Method for Approximate Extensive-Form Perfect Equilibrium

2017 ◽  
Author(s):  
Christian Kroer ◽  
Gabriele Farina ◽  
Tuomas Sandholm
Keyword(s):  
Nash Equilibrium ◽  
Imperfect Information ◽  
Large Scale ◽  
Nash Equilibria ◽  
Convex Polytope ◽  
Solution Concept ◽  
Extensive Form ◽  
Game Tree ◽  
Equilibrium Refinements ◽  
Perfect Equilibria

Nash equilibrium is a popular solution concept for solving imperfect-information games in practice. However, it has a major drawback: it does not preclude suboptimal play in branches of the game tree that are not reached in equilibrium. Equilibrium refinements can mend this issue, but have experienced little practical adoption. This is largely due to a lack of scalable algorithms.Sparse iterative methods, in particular first-order methods, are known to be among the most effective algorithms for computing Nash equilibria in large-scale two-player zero-sum extensive-form games. In this paper, we provide, to our knowledge, the first extension of these methods to equilibrium refinements. We develop a smoothing approach for behavioral perturbations of the convex polytope that encompasses the strategy spaces of players in an extensive-form game. This enables one to compute an approximate variant of extensive-form perfect equilibria. Experiments show that our smoothing approach leads to solutions with dramatically stronger strategies at information sets that are reached with low probability in approximate Nash equilibria, while retaining the overall convergence rate associated with fast algorithms for Nash equilibrium. This has benefits both in approximate equilibrium finding (such approximation is necessary in practice in large games) where some probabilities are low while possibly heading toward zero in the limit, and exact equilibrium computation where the low probabilities are actually zero.

scholarly journals Coarse Correlation in Extensive-Form Games

2020 ◽  
Vol 34 (02) ◽  
pp. 1934-1941
Author(s):  
Gabriele Farina ◽  
Tommaso Bianchi ◽  
Tuomas Sandholm
Keyword(s):  
Normal Form ◽  
Saddle Points ◽  
Solution Concept ◽  
Correlated Equilibrium ◽  
Extensive Form ◽  
Extensive Form Games ◽  
Rational Agents ◽  
Correlation Models ◽  
Correlated Equilibria ◽  
Special Case

Coarse correlation models strategic interactions of rational agents complemented by a correlation device which is a mediator that can recommend behavior but not enforce it. Despite being a classical concept in the theory of normal-form games since 1978, not much is known about the merits of coarse correlation in extensive-form settings. In this paper, we consider two instantiations of the idea of coarse correlation in extensive-form games: normal-form coarse-correlated equilibrium (NFCCE), already defined in the literature, and extensive-form coarse-correlated equilibrium (EFCCE), a new solution concept that we introduce. We show that EFCCEs are a subset of NFCCEs and a superset of the related extensive-form correlated equilibria. We also show that, in n-player extensive-form games, social-welfare-maximizing EFCCEs and NFCCEs are bilinear saddle points, and give new efficient algorithms for the special case of two-player games with no chance moves. Experimentally, our proposed algorithm for NFCCE is two to four orders of magnitude faster than the prior state of the art.

First-Principles Theory of Polarization in Ferroelectrics

1992 ◽  
Vol 291 ◽  
Author(s):  
R. Resta ◽  
M. Posternak ◽  
A. Baldereschi
Keyword(s):  
Spontaneous Polarization ◽  
First Principles ◽  
Ferroelectric Materials ◽  
Recent Experimental Data ◽  
Modern Theory ◽  
Rigid Core ◽  
Novel Approach ◽  
Prototype Structure ◽  
Effective Charges ◽  
The Difference

ABSTRACTWe outline a modern theory of the spontaneous polarization P in pyroelectric and ferroelectric materials. Although P itself isnot an observable, the difference ΔP between two crystal states can indeed be measured and calculated. We define P as the difference between the polar structure and a suitably chosen nonpolar prototype structure. We previously proposed and implemented a supercell scheme in order to evaluate P in pyroelectric BeO; here we adopt an approach recently developed by King-Smith and Vanderbilt, where ΔP is obtained from the computation of Berry's phases, with no use of supercells. We apply this novel approach, which is numerically very convenient, in order to revisit our previous work on BeO. We then perform a first-principles investigation of the spontaneous polarization P of KNbO3 in its tetragonal phase, which is a well studied perovskite ferroelectric. Our calculated P value confirms the most recent experimental data. The polarization is linear in the ferroelectric distortion; the Born effective charges show strong variations from nominal ionic values, and a large inequivalence of the 0 ions. Only the highest nine valence-band states (O 2p) contribute to P, while all the other states behave as rigid core states.

scholarly journals Prudent Rationalizability in Generalized Extensive-Form Games

2011 ◽  
Author(s):  
Aviad Heifetz ◽  
Martin Meier ◽  
Burkhard C. Schipper
Keyword(s):  
Extensive Form ◽  
Extensive Form Games
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