Iterated Prisoner’s Dilemma on Alliance Network

1. Iterated Prisoner’s Dilemmaon Alliance Network Tomoki Furukawazono* Yusuke Takada** Takashi Iba** *Graduate School of Media and Governance, Keio University **Faculty of Policy Management, Keio University

2. Social System Analysis with the concept of “Complex System” and “Autopoietic System” • Complex System • Society as the swarm / group of agents and its interactions. • Autopoietic System • Society as the nexus of “communication” • The difference between Social System / Social Structure • Proposed by Niklas Luhmann

3. Understanding the social systems through modeling and simulation

4. “PlatBox” as a new tools for thinking • PlatBox Simulator • a software platform to execute and to analyze the agent-based social simulations. • Component Builder • The tool for designing the model component plugged into PlatBox Simulator. • The modeler can develop his/her simulation program just by drawing model diagrams in the modeling language (UML).

5. “PlatBox” as a new tools for thinking • Multi-Agent simulation on Social Network of agents • Dynamics on the social network • Dynamics of the social network

6. Alliance Network This research, will examine how the cooperation within nations emerges in the alliances and helps create a stable network. ① Alliance can be considered as network Nation ⇒ Node, Alliance ⇒ Edge NATO Japan-U.S. Alliance

7. ②Alliance Dilemma (Snyder 1984) Most cases end up in a dilemma e.g.) Japan-US Alliance It is ideal for allies to give full support for each other e.g.) Franco-Russian Alliance (1892-1917) Abandoning allies creates a chance to attack for others. From this payoff matrix, Alliance Dilemma = Prisoner’s Dilemma

8. Experiment To see the difficulty of maintaining the alliance Alliance forms a network + Alliance Dilemma = Prisoner’s Dilemma Iterated Prisoner’s Dilemma game will be played on the Alliance Network ⇒

9. The Simulation Model Based on Santos and Pacheco (2005) ①Dilemma Game Pｙ points Payoff depending on its own strategy Px points ②Strategy Change Change strategy with this percentage ＜ IF Px Pｙ ＞ Maintain its strategy Px Pｙ Repeat this process

10. Parameter ●Evaluation Year ：　１９５２～２０００ ●Percentage of initial cooperators ：　５０％ ●Payoff for free riders(ｂ)　：　１～２ ●Steps：２１００ ●Alliance Data from Correlates of War http://cow2.la.psu.edu/

11. Simulation Results The results show high fraction of cooperators in the years 1964-1976 WHY?? Fraction of cooperators Shows the great influence of the free-riders in an Alliance Network

12. YEAR１９７６ step2 step1 step0 Betrayer increases but U.K. and France stay cooperative

13. step31 step32 step33 Betrayer decreases due to U.K. and France

14. Analysis of Inner Mechanism Fraction of cooperators steps Nations with its own multilateral alliances works to maintain the cooperation

15. Conclusion & Consideration In the Alliance network that Japan belonged to after WWII, The betrayal in the alliance causes a great effect not only within the alliance but to the whole network For the Alliance network, the existence of multilateral alliance, such as of French or British, helps to maintain the cooperation within the alliance network

16. thank you very mucharigato!