Venanzi, Matteo
(2009)
Trust, Kinship and Locality in the Iterated Prisoner's Dilemma.
*University of Rome "La Sapienza", Department of Computer Engineering (DIS), Masters Thesis*.

## Abstract

The Prisoner's Dilemma is maybe the best-known paradox in Game Theory. In this game, a player meets another player, and must choose to cooperate or defect: the best outcome for player i would be achieved if i defected while the opponent j cooperated, which would be the worst outcome for player j; both players would prefer mutual cooperation over mutual defection; and finally, the scenario is "symmetric". From the perspective of game theory, the rational choice in the prisoners dilemma is for both players to defect. It is called a "dilemma" because in fact both players would prefer mutual cooperation { but this outcome is impossible, because if one player cooperates, the other would rather defect. [Axelrod 1984] ran a tournament in which players played the prisoners dilemma against a number of opponents in a series of rounds (the "iterated prisoners dilemma"). He found that "cooperative" game playing strategies could flourish in this tournament if they were given the opportunity to encounter other cooperative strategies. This study is aimed at investigating the following issues around the iterated prisoners dilemma: (i) Trust: Suppose every agent is equipped with a value tw indicating how trustworthy it is; what happens if we take account of such a value in making decisions; how does this affect the dynamics of cooperation/defection? (ii) Kinship: Suppose we have a model of "family distance", so that agents are classified into families, being less likely to cooperate with those that are more distant in family terms. How do such concerns affect the dynamics of cooperation? (iii) Locality: Suppose agents are arranged on a graph, and retrieve trust information by querying and using trust of their neighbours. How does graph topology affect the dynamics of cooperation? E.g. is it the case that "gregarious" agents (with lots of neighbours) perform much better than "lonely" agents (with only 1 neighbour)? We will investigate through experiments the notions of Trust and Reliability applied to the Prisoner's Dilemma context, under multiple aspects. We will review works related to these topics in order to introduce some efficient solutions for dealing with the above issues.

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