Iba Laboratory

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

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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

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Understanding the social systems through modeling and simulation

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“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).

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“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 LaboratoryAlliance 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

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②Alliance Dilemma (Snyder 1984)

It is ideal for allies to give full support for each other e.g.) Franco-Russian Alliance (1892-1917)

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

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ExperimentTo 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

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The Simulation Model

①Dilemma Game

Px points

P ｙ points

②Strategy Change

P ｙPx ＞P ｙPx ＜IF

Change strategy with this percentage

Maintain its strategy

Repeat this process

Based on Santos and Pacheco (2005)

Payoff depending on its own strategy

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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 http://cow2.la.psu.edu/

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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 1964-1976 WHY??

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step0

step1step2

Betrayer increases but U.K. and France stay cooperative

YEAR１９７６

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Betrayer decreases due to U.K. and France

step31 step32 step33

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Analysis of Inner Mechanism

Fraction of cooperators

steps

Nations with its own multilateral alliances works to maintain the cooperation

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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

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thank you very mucharigato!