The Iterated Prisoner's Dilemma Competition:
Celebrating the 20^th Anniversary

Breaking News:

• Call For Chapters for updated book

• Latest Results

You and a friend have committed a crime and have been caught. You are being held in separate cells. You are both offered a deal but have to decide what to do. But you are not allowed to communicate with your partner and you will not be told what they have decided until you have made a decision.
Essentially the deal is this.

• If you confess and your partner denies taking part in the crime, you go free and your partner goes to prison for five years.
• If your partner confesses and you deny participating in the crime, you go to prison for five years and yor partner goes free.
• If you both confess you will serve four years each.
• If you both deny taking part in the crime, you both go to prison for two years.

What do you do?

The dilemma you are faced with is that it is better for you to confess, UNLESS you both deny taking part in the crime. BUT, if you think that you partner will deny taking part, then you CONFESS and go free. See the dilemma?

To read another (better!) description of the prisoners dilemma see the Stanford Encyclopedia of Philosophy entry and, to play a game, visit http://www.princeton.edu/~mdaniels/PD/PD.html.

Another way of looking at the Prisoners Dilemma can be found here. This is the definition used in this competition.

The Competition

We are planning a series of competitions (the first was held at the Congress of Evolutionary Computation in July 2003, the second will be held in April 2005) to celebrate, pay tribute to and update the competitions run by Axelrod [AXE84]. Importantly we aim to provide the environment and data to allow researchers to conduct investigations into the latest developments surrounding the iterated prisoners dilemma. The competitions we originally held were 1-3, below. For the second set of competitions, we have introduced a new category (number 4, below).

1. Re-run the original experiment of Axelrod. We aim to see if a tit-for-tat strategy still dominates or whether somebody can develop a better strategy taking into account that there has been 20 years since the original competition (for example, tit-for-2-tats was claimed to be better than tit-for-tat). In addition, we would expect many more entries that the 62 received by Axelrod (largely due to the internet), thus giving us access to much more data.
2. Organise a competition that has noise in the data. That is, a signal to cooperate or defect could be mis-executed.
3. Allow competitors to submit a strategy to an IPD that has more than one player and more than one payoff, that is, multi player and multi-choice.
4. This competition will mirror the original competition of Axelrod. That is, the rules are

• We will only allow one entrant per competitor and we will not allow collusion between different competitors.
• The only strategy that will be introduced by the tournament organisers will be RANDOM.
• Each strategy will also play against its twin.
• Every tournament will comprise the same number of moves, which will be unknown to the entrants. We will run each tournament 5 fives times using a different, fixed number of moves. In the original (second round) tournament, Axelrod used a 0.00346 probability of ending the game at each move. In fact, he drew the random samples before each game and then “fixed” the number of moves at 63, 77, 151, 156 and 308. We will use a similar scheme, but will not use the same game lengths.
• The payoff matrix will be the one used in the original Axelrod competition. That is, both players will be awarded 3 points for mutual cooperation, 1 point will be awarded for mutual defection and if one player defects and the other cooperates then the defector receives 5 points and the co-operator receives 0 points.
• We will impose a time limit on the amount of time that a player can use to make a move. This will be set at 2 seconds. THIS IS DIFFERENT TO THE ORIGINAL TOURNAMENT, but we believe it is necessary to avoid infinite loops.
• We will insist on being given a description of the strategy, and source code, for all the strategies submitted. The source code will NOT be made publicly available. However, we have to insist on the source code so that we can monitor for collusion
  

More details about the competition can be seen here. Please note that we wish to make this competition open to as many people as possible - not just the academic community.

Please note: If you submitted a strategy(s) to the first competition, they will automatically be entered for the 2nd competition. In addition, if you only entered a single strategy, this will automatically be entered into competition 4, see above

Important dates can be seen here.

Other Details

• This competition is being jointly organised by Graham Kendall, Paul Darwen and Xin Yao.
• It will culminate at The Congress on Evolutionary Computation Conference (CEC'04) in June 2004.
• This work is being supported by the UK's The Engineering and Physical Sciences Research Council (EPSRC)