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Poster

No-Regret Learning and Mixed Nash Equilibria: They Do Not Mix

Emmanouil-Vasileios Vlatakis-Gkaragkounis · Lampros Flokas · Thanasis Lianeas · Panayotis Mertikopoulos · Georgios Piliouras

Poster Session 6 #1866

Keywords: [ Algorithms -> Semi-Supervised Learning; Applications ] [ Computer Vision; Deep Learning ] [ Computational Photography ] [ Applications ]


Abstract:

Understanding the behavior of no-regret dynamics in general N-player games is a fundamental question in online learning and game theory. A folk result in the field states that, in finite games, the empirical frequency of play under no-regret learning converges to the game’s set of coarse correlated equilibria. By contrast, our understanding of how the day-to-day behavior of the dynamics correlates to the game’s Nash equilibria is much more limited, and only partial results are known for certain classes of games (such as zero-sum or congestion games). In this paper, we study the dynamics of follow the regularized leader (FTRL), arguably the most well-studied class of no-regret dynamics, and we establish a sweeping negative result showing that the notion of mixed Nash equilibrium is antithetical to no-regret learning. Specifically, we show that any Nash equilibrium which is not strict (in that every player has a unique best response) cannot be stable and attracting under the dynamics of FTRL. This result has significant implications for predicting the outcome of a learning process as it shows unequivocally that only strict (and hence, pure) Nash equilibria can emerge as stable limit points thereof.

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