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Information on Doing Research with SimSociety

Some preliminaries for the iterated prisoners dilemma game simulation (SimSociety)

Recall the PD game

		Player B
Player A		Coop	Defect
	Coop	c,c	c,d
	Defect	d,c	d,d

Where

1. c,c is mutual cooperation
2. c,d A cooperates and B defects
3. d,c A defects and B cooperates
4. d,d both defect – mutual defection

Now we can characterize a set of IPD game strategies by indicating the probabilities that a player will cooperate given each of the 4 outcomes (noted above) of the game from the last or prior iteration and denoting for the very first iteration whether the player will choose to cooperate or defect so lets denote

1. P(1) as the probability of cooperating on the current iteration given that c,c was the outcome from the last or prior iteration
2. P(2) as the probability of cooperating on the current iteration given that c,d was the outcome from the last or prior iteration
3. P(3) as the probability of cooperating on the current iteration given that d,c was the outcome from the last or prior iteration
4. P(4) as the probability of cooperating on the current iteration given that d,d was the outcome from the last or prior iteration

Thus as strategy can be defined as

[ P(1), P(2), P(3), P(4)]

with the addition of a cooperate or defect choice stipulation on the first iteration

So a strategy that always cooperates (All-c) can be represented as – cooperate on the first round and

[1,1,1,1]

A strategy that always defects (All-D) can be represented as – defect on the first round and

[0,0,0,0]

Some classic strategies

Tit-for-Tat (TFT) cooperate on the first round and then choose whatever the opponent chose in the previous round

[1,0,1,0]

Pavlov – win stay – lose change – if you like the result from the last round continue doing what you are doing – if you do not then change

Cooperate on the first round and then

[1,0,0,1]

Grim – cooperate on the first round and then cooperate as long as the opponent cooperates – If the opponent defects then defect from that point forward

Generous TFT cooperate the first time and with 100% prob reward prior cooperation by the opponent – either c,c or d,c and with some probability cooperate after you instigated defection c,d and if there is mutual defection d,d

[1, r,1,r] where r is between 0.0 and 1.0

Mean TFT – defect on the first round – always punish prior defection and sometimes but not always reward prior cooperation

[q,0,q,0] where q is between 0.0 and 1.0

Some important characteristics of strategies

We can characterize strategies as

What kinds of strategies must agents use to survive and succeed in a world of anarchic self interested agents

How does cooperation develop in such a world – Why? What strategies seems to make this work and why?

What kinds of strategies seem to be able to maintain cooperation?

What kinds of strategies must agents use to survive and succeed in a world of anarchic self-interested agents

How does cooperation develop in such a world – Why? What strategies seems to make this work and why?

What kinds of strategies seem to be able to maintain cooperation?

Recall some important characteristics of strategies

We can characterize strategies as

A strategy ---- Do strategies need to be nice to generate and maintain cooperation?

Are some strategies too nice to generate and maintain cooperation?

How important is retaliation and forgiveness?

Can exploiters succeed – that is do well by mixing in with cooperative strategies but not either getting wiped out or crashing the cooperative system?

To answer these questions think of a systematic way of assessing various strategies

Say start with All C – the epitome of nice -- Can it survive and prosper with other nice strategies – run mixes with All C and say TFT – can it survive with some nasty and exploitative – run some All C mixes with All-D, Grim, MFTF, and Pavlov

Can forgiving and/or retaliatory strategies generate cooperation and can they withstand and maintain cooperation with exploiters and nasty strategies

Run mixes of TFT, Pavlov and GFFT vs exploiters like All-D, MTFT, and Grim,

Reading AssignmentsSim Society Research Info.Paper AssignmentLecture Outlines

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