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

Iba Laboratory 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

Iba Laboratory Understanding the social systems through modeling and simulation

Iba Laboratory “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).

Iba Laboratory “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

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

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

Iba Laboratory 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

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

Iba Laboratory Parameter ●Percentage of initial cooperators ： ５０％ ●Payoff for free riders( ｂ ) ： １～２ ●Evaluation Year ： １９５２～２０００ ●Steps ：２１００ ●Alliance Data from Correlates of War

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

Iba Laboratory step0 step1 step2 Betrayer increases but U.K. and France stay cooperative YEAR １９７６

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

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

Iba Laboratory 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

Iba Laboratory thank you very much arigato!