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well-known criterion of distributive justice, a fair society should be organized so as to
admit economic inequalities to the extent that they are beneficial to the less advantaged
agents. 4 Following Rawls' interpretation, an agent's moral motivation should coincide
with the goal of maximizing the collective utility represented by the individual utility
of the less advantaged agent.
Definition 6 (Normal form game with moral values based on Rawls' view). A nor-
mal form game with moral values
Γ + =
( N
,{
S i } i N ,{
U i } i N ,{
I i } i N ) is based on Rawls'
view of morality if and only if for all i
N:
I i ( s )
=
min
j
U j ( s )
(6)
N
3
Simulation
We have developed an agent-base model in order to test the various hypothesis on the
model. In this article, we mainly investigate the influence of the way to compute ide-
ality and the influence of the guilt aversion on agent behaviors. To this purpose, we
have chosen the standard Prisoner's Dilemna [21] as frame of the interactions between
agents.
The model is implemented using the GAMA platform 5 [26], an open-source generic
agent-based modeling and simulation platform. It provides an intuitive modeling lan-
guage with high-level primitives to define agents and their environment. GAMA has
been used successfully to develop a large spectrum of models, from simple and abstract
models (as the one presented here) to large-scale models (including lot of different kinds
of agents and needing a huge amount of data).
3.1
Model Description
The following paragraphs describe in greater details the computational implementation
of the model described in section 2.1.
Global Variables and Parameters
The game that agents will play is the same for all agents, it (and in particular the payoff
matrix) is thus a global variable. It is a standard Prisoner's Dilemma whose payoffs are
the following: R = 2, T = 3, S = 0 and P = 1 6 . Being a standard Prisoner's Dilemma type
of game, each agent has two possible strategies: cooperate ( C ) or defect ( D ). In addition,
as we will see, we shall modify the ideality computation method ( i.e .Harsanyi'sand
4 It has to be noted that Rawls' theory of justice is specified in terms of justice over primary
goods. Rawls' list of primary goods includes for instance basic liberties and rights, freedom of
movement and free choice of occupation, income and wealth, the social bases of self-respect.
This difference is however beyond the scope of the present article. See [25] for a discussion
on this issue.
5 http://code.google.com/p/gama-platform/
6
Although for this first version of the article, we employ the standard payoffs mentioned, the
four payoff values might be modified, as they are parameters of the simulation.
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