The Model

The Prisoner's Dilemma (PD) was described by Merrill Flood and Melvin Dresher, and is closely related to game theory. This implementation of the model based on the NetLogo version, which may give a good opportunity to compare the languages.

Two suspects are arrested by the police. The police have insufficient evidence for a conviction, and, having separated both prisoners, visit each of them to offer the same deal. If one testifies (defects from the other) for the prosecution against the other and the other remains silent (cooperates with the other), the betrayer goes free and the silent accomplice receives the full 10-year sentence. If both remain silent, both prisoners are sentenced to only six months in jail for a minor charge. If each betrays the other, each receives a five-year sentence. Each prisoner must choose to betray the other or to remain silent. Each one is assured that the other would not know about the betrayal before the end of the investigation. How should the prisoners act?

In the Iterated  Prisoner's Dilemma (IPD), the game is played repeatedly. In the current Agent-based simulation there are several agents playing IPD, and their score is cumulated each turn using the following rules:

The exported Fables project can be downloaded here.
To import the model, select File --> Import and chose the Fables / Fables Project wizard. 

How does it work?

There is a fixed number of agents playing PD each simulation step. They choose a partner randomly from the list of agents who haven't played in the current simulation turn.

By default, there are 10 agents playing with each of the following strategies:

• Cooperative: always cooperates
• Defective: always defects
• Random: choses its actions randomly
• Tit for Tat: if the current partner was cooperating last time (or haven't played with it at all) then cooperates, otherwise defects
• Unforgiving: cooperates until the partner defects, always defecting afterwards.

The chart of the simulation shows the cumulated scores for each group of agents.

References

The Prisoner's dilemma
From Wikipedia, the free encyclopedia

Dresher, M. (1961). The Mathematics of Games of Strategy: Theory and Applications Prentice-Hall, Englewood Cliffs, NJ.

Flood, M.M. (1952). Some experimental games. Research memorandum RM-789. RAND Corporation, Santa Monica, CA.