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Game Transformations That Preserve Nash Equilibria or Best-Response Sets

Published: 06 May 2024 Publication History

Abstract

In the full version of this paper, we investigate under which conditions normal-form games are (guaranteed) to be strategically equivalent. First, we show for N-player games (N ≥ 3) that (a) it is NP-hard to decide whether a given strategy is a best response to some strategy profile of the opponents, and that (b) it is co-NP-hard to decide whether two games have the same best-response sets.
We then turn our attention to equivalence-preserving game transformations. It is a widely used fact that a positive affine (linear) transformation of the utility payoffs neither changes the best-response sets nor the Nash equilibrium set. We investigate which other game transformations also possess either of the following two properties when being applied to an arbitrary N-player game (N ≥ 2): (i) The Nash equilibrium set stays the same; (ii) The best-response sets stay the same.
For game transformations that operate player-wise and strategy-wise, we prove that (i) implies (ii) and that transformations with property (ii) must be positive affine. The resulting equivalence chain highlights the special status of positive affine transformations among all the transformation procedures that preserve key game-theoretic characteristics.

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cover image ACM Conferences
AAMAS '24: Proceedings of the 23rd International Conference on Autonomous Agents and Multiagent Systems
May 2024
2898 pages
ISBN:9798400704864

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International Foundation for Autonomous Agents and Multiagent Systems

Richland, SC

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Published: 06 May 2024

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Author Tags

  1. best responses
  2. game transformation
  3. nash equilibrium
  4. positive affine linear transformation
  5. strategic equivalence

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  • Cooperative AI Foundation Polaris Ventures and Jaan Tallinn's donor-advised fund at Founders Pledge

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