Double-oracle Algorithm for Computing an Exact Nash Equilibrium in Zero-sum Extensive-form Games
We investigate an iterative algorithm for computing an exact Nash equilibrium in two-player zero-sum extensive-form games with imperfect information. The approach uses the sequence-form representation of extensive-form games and the double-oracle algorithmic framework. The main idea is to restrict the game by allowing the players to play only some of the sequences of available actions, then iteratively solve this restricted game, and exploit fast best-response algorithms to add additional sequences to the restricted game for the next iteration. In this paper we (1) extend the sequence-form double-oracle method to be applicable on non-deterministic extensive-form games, (2) present more efficient methods for maintaining valid restricted game and computing best response sequences, and finally we (3) provide theoretical guarantees of the convergence of the algorithm to a Nash equilibrium. We experimentally evaluate our algorithm on two types of games: a search game on a graph and simplified variants of Poker. The results show significant running-time improvements compared to the previous variant of the double-oracle algorithm, and demonstrate the ability to find an exact solution of much larger games compared to solving full linear program for the complete game.