In a turtle tournament each turtle picks a random neighbor and plays a mutual dilemma game with him.
In a mutual dilemma game two players, A and B, are presented
with a mutual dilemma. Each must choose one of two options: fight or flee,
cooperate or defect, hold 'em or fold 'em, etc. The choice may be based on strategy and history,
but is made without knowing the opponent's choice.
After the choices are made, each player is awarded points
based on the game's payoff matrix:
|
Payoffs |
B |
||
|
FALSE |
TRUE |
||
|
A |
FALSE |
a1/b1 |
a2/b2 |
|
TRUE |
a3/b3 |
a4/b4 |
|
The a3/b3 entry indicates that if A chooses TRUE and B chooses FALSE, then A receives a3 points and B receives b3 points.
A turtle's fitness is simply the sum of all of his payoff points.
When a turtle is updated, he randomly picks a nearby turtle and plays a game with him:
to play-game-with [candidate]
let my-choice choice? candidate
let candidate-choice [choice? myself]
of candidate
update-attributes candidate my-choice
candidate-choice
end
The
choice can be based on knowledge of the candidate's history and the strategy
used by the active turtle. For now the choice is random:
to-report choice? [candidate]
report (random 2) < 1 ; for now
end
The
update-attributes procedure updates the executor's fitness, number of games
played, and history (i.e., candidate's choice).
The
payoffs are global variables:
globals [
payoff-a1 ; payoff for A if A & B chose TRUE
payoff-a2 ; payoff for A if A chooses TRUE and B FALSE
payoff-a3 ; payoff for A if A chooses FALSE and B TRUE
payoff-a4 ; payoff for A if A & B choose FALSE
payoff-b1 ; payoff for B if A & B chose TRUE
payoff-b2 ; payoff for B if A chooses TRUE and B FALSE
payoff-b3 ; payoff for B if A chooses FALSE and B TRUE
payoff-b4 ; payoff for B if A & B choose FALSE
]
In a PD tournament, turtles are constantly playing PD with each other. They make their choice—to cheat or cooperate—based on some strategy.