New Winning Strategies for the Iterated Prisoner's Dilemma

Abstract

In the iterated prisoner’s dilemma game, new successful strategies are regularly proposed especially outperforming the well-known tit for tat strategy. New forms of reasoning have also recently been introduced to analyse the game. They lead William Press and Freeman Dyson to a double infinite family of strategies that - theoretically - should all be good strategies. In this paper, we study and confront using severals experimentation the main strategies introduced since the discovery of tit for tat. We make them play against each other in varied and neutral environments. We use the complete classes method that leads us to the formulation of four new simple strategies with surprising results. We present massive experiments using simulators specially developed that allow us to confront up to 2000 strategies simultaneously, which had never been done before. Our results identify without any doubt the most robust strategies among those so far identified. This work identifies new systematic, reproductible and objective experiments suggesting several ways to design strategies that go a step further, and a step in the software design technology for good strategies in iterated prisoner’s dilemma and multi-agent systems in general.