Equilibrium solutions of three player Kuhn poker with $N>3$ cards: A new numerical method using regularization and arc-length continuation

Abstract: We study the equilibrium solutions of three player Kuhn poker with $N>3$ cards. We compute these solutions as a function of the initial pot size, $P$, using a novel method based on regularizing the system of polynomial equations and inequalities that defines the solutions, and solving the resulting system of nonlinear, algebraic equations using a combination of Newton's method and arc-length continuation. We find that the structure of the equilibrium solution curve is very complex, even for games with a small number of cards. Standard three player Kuhn poker, which is played with $N=4$ cards, is qualitatively different from the game with $N>4$ cards because of the simplicity of the structure of the value betting and bluffing ranges of each player. When $N>5$, we find that there is a new type of equilibrium bet with midrange cards that acts as a bluff against one player and a value bet against the other.