I mentioned before that the NetLogo models library has a number of
models related to the prisoner's dilemma. this is one of them they're gonna look
at now
it's called PD n person iterated
and you can download it from our course materials page. this model
unlike the one we've just been talking about has
multiple agents cure all the different agents
each one them play a particular strategy
for the prisoner's dilemma here the strategies
random which means you either cooperator defected random
each time always cooperate this one
defect always defact, tit-for-tat we talked about
unforgiving this strategy
always cooperate until its opponent
defects at which time it will always defect Trevor
never forgives the defection unknown they're sure of these right now but
you can actually feel in your own strategy
by going to the code tab and seen
the comment this is filling your strategy here for
unknown word I can use that right now LP
part of the homework but we're going to do is look at
we have 10 of each strategies and we're gonna watch them
interact so I gonna go
speed them up a little bit you see they're moving around when they come
close enough
the interact can play around with the prisoner's dilemma
according to their strategy each time there's a game
you see the payoffs appear next to the agents
you can also see the average payoff for each type the strategy here
see that defect strategy of always defect
his the highest second is random
then tit-for-tat than in unforgiving and cooperators
lowest wanna rock but if we speed up and play for a while
we'll see if that actually changes overtime
you can make it really fast and you see that defect
actually starts to go down and
defect actually goes down and
to tit-for-tat goes above defect. Okay so anyway
I'm going to give you some exercises to do with the homework using this model
which will perhaps give you some insight into why these kinds of dynamics are
happening
the conclusions that Axelrod drew from all of these tournaments
where the following: strategy seated well
were nice they were never the first to defect
they were forgiving that is they were willing to cooperate if corporations
offered
they were retaliatory that is they were willing to defect
if others defected against them and he added one more condition to be clear
that is be transparent about what your strategy is make it easy to infer
so that your partner knows how to react to what you did
it can predict what your next move is going to be it knows you're going to be
retaliatory or forgiving
and these are the conditions which at least in the prisoner's dilemma context
for what induce reciprocal cooperation in an iterated prisoner's dilemma game
and several people have proposed these as general
attributes that strategies should have in the real world for trying to induce
cooperation
in arms race like situations and of course tit-for-tat
has all these attributes that's all I'm gonna say about the prisoner's dilemma
it's a huge field actually with many many variations
and I've put some references up on the course
materials page that will give you a feeling for
the different kinds are variations Axelrod's book the complexity of
cooperation talks about many of them
and summer the optional homework assignments will have you read about
some them