Grim trigger

Grim trigger (also called the grim strategy or just grim) is a trigger strategy in game theory for a repeated game, such as an iterated prisoner's dilemma. Initially, a player using grim trigger will cooperate, but as soon as the opponent defects (thus satisfying the trigger condition), the player using grim trigger will defect for the remainder of the iterated game. Since a single defect by the opponent triggers defection forever, grim trigger is the most strictly unforgiving of strategies in an iterated game.

Note that tit for tat, the commonly accepted optimal iterated game strategy, is also a trigger strategy, except that unlike grim trigger, it only "remembers" one move previous when determining whether to cooperate or defect.

In Robert Axelrod's book "The Evolution of Cooperation", grim trigger is called "FRIEDMAN" (James Friedman uses the concept in the 1971 paper: "A Non-cooperative Equilibrium for Supergames").

In iterated prisoner's dilemma strategy competitions, Grim Trigger does poorly even without noise, and adding signal errors makes it even worse. It has many defects [cite web | quote = In sum, Grim Trigger seems like a good idea, but isn’t. | url = http://www.fordschool.umich.edu/research/papers/PDFfiles/00-003.pdf | title = On Six Advances in Cooperation Theory | first = Robert | last = Axelrod | year = 2000 | accessdate = 2007-11-02 (page 13)] but it primarily suffers from the inability to threaten permanent defection.

ee also

* Folk theorem (game theory)

References