ncase.me-trust/js/sims/PD.js

var PD = {};
PD.COOPERATE = "COOPERATE";
PD.CHEAT = "CHEAT";

PD.PAYOFFS_DEFAULT = {
	P: 0, // punishment: neither of you get anything
	S: -1, // sucker: you put in coin, other didn't.
	R: 2, // reward: you both put 1 coin in, both got 3 back
	T: 3 // temptation: you put no coin, got 3 coins anyway
};

PD.PAYOFFS = PD.PAYOFFS_DEFAULT;

PD.NOISE = 0.05;

PD.getPayoffs = function(move1, move2){
	var payoffs = PD.PAYOFFS;
	if(move1==PD.CHEAT && move2==PD.CHEAT) return [payoffs.P, payoffs.P]; // both punished
	if(move1==PD.COOPERATE && move2==PD.CHEAT) return [payoffs.S, payoffs.T]; // sucker - temptation
	if(move1==PD.CHEAT && move2==PD.COOPERATE) return [payoffs.T, payoffs.S]; // temptation - sucker
	if(move1==PD.COOPERATE && move2==PD.COOPERATE) return [payoffs.R, payoffs.R]; // both rewarded
};

PD.playOneGame = function(playerA, playerB){

	// Make your moves!
	var A = playerA.play();
	var B = playerB.play();

	// Noise: random mistakes, flip around!
	if(Math.random()<PD.NOISE) A = ((A==PD.COOPERATE) ? PD.CHEAT : PD.COOPERATE);
	if(Math.random()<PD.NOISE) B = ((B==PD.COOPERATE) ? PD.CHEAT : PD.COOPERATE);
	
	// Get payoffs
	var payoffs = PD.getPayoffs(A,B);

	// Remember own & other's moves (or mistakes)
	playerA.remember(A, B);
	playerB.remember(B, A);

	// Add to scores (only in tournament?)
	playerA.addPayoff(payoffs[0]);
	playerB.addPayoff(payoffs[1]);

};

PD.playRepeatedGame = function(playerA, playerB, turns){

	// I've never met you before, let's pretend
	playerA.resetLogic();
	playerB.resetLogic();

	// Play N turns
	for(var i=0; i<turns; i++){
		PD.playOneGame(playerA, playerB);
	}

};

PD.playOneTournament = function(agents, turns){

	// Reset everyone's coins
	for(var i=0; i<agents.length; i++){
		agents[i].resetCoins();
	}

	// Round robin!
	for(var i=0; i<agents.length; i++){
		var playerA = agents[i];
		for(var j=i+1; j<agents.length; j++){
			var playerB = agents[j];
			PD.playRepeatedGame(playerA, playerB, turns);
		}	
	}

};

///////////////////////////////////////////////////////
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///////////////////////////////////////////////////////

function Logic_tft(){
	var self = this;
	var otherMove = PD.COOPERATE;
	self.play = function(){
		return otherMove;
	};
	self.remember = function(own, other){
		otherMove = other;
	};
}

function Logic_tf2t(){
	var self = this;
	var howManyTimesCheated = 0;
	self.play = function(){
		if(howManyTimesCheated>=2){
			return PD.CHEAT; // retaliate ONLY after two betrayals
		}else{
			return PD.COOPERATE;
		}
	};
	self.remember = function(own, other){
		if(other==PD.CHEAT){
			howManyTimesCheated++;
		}else{
			howManyTimesCheated = 0;
		}
	};
}

function Logic_grudge(){
	var self = this;
	var everCheatedMe = false;
	self.play = function(){
		if(everCheatedMe) return PD.CHEAT;
		return PD.COOPERATE;
	};
	self.remember = function(own, other){
		if(other==PD.CHEAT) everCheatedMe=true;
	};
}

function Logic_all_d(){
	var self = this;
	self.play = function(){
		return PD.CHEAT;
	};
	self.remember = function(own, other){
		// nah
	};
}

function Logic_all_c(){
	var self = this;
	self.play = function(){
		return PD.COOPERATE;
	};
	self.remember = function(own, other){
		// nah
	};
}

function Logic_random(){
	var self = this;
	self.play = function(){
		return (Math.random()>0.5 ? PD.COOPERATE : PD.CHEAT);
	};
	self.remember = function(own, other){
		// nah
	};
}

// Start off Cooperating
// Then, if opponent cooperated, repeat past move. otherwise, switch.
function Logic_pavlov(){
	var self = this;
	var myLastMove = PD.COOPERATE;
	self.play = function(){
		return myLastMove;
	};
	self.remember = function(own, other){
		myLastMove = own; // remember MISTAKEN move
		if(other==PD.CHEAT) myLastMove = ((myLastMove==PD.COOPERATE) ? PD.CHEAT : PD.COOPERATE); // switch!
	};
}

// TEST by Cooperate | Cheat | Cooperate | Cooperate
// If EVER retaliates, keep playing TFT
// If NEVER retaliates, switch to ALWAYS DEFECT
function Logic_prober(){

	var self = this;

	var moves = [PD.COOPERATE, PD.CHEAT, PD.COOPERATE, PD.COOPERATE];
	var everCheatedMe = false;

	var otherMove = PD.COOPERATE;
	self.play = function(){
		if(moves.length>0){
			// Testing phase
			var move = moves.shift();
			return move;
		}else{
			if(everCheatedMe){
				return otherMove; // TFT
			}else{
				return PD.CHEAT; // Always Cheat
			}
		}
	};
	self.remember = function(own, other){
		if(moves.length>0){
			if(other==PD.CHEAT) everCheatedMe=true; // Testing phase: ever retaliated?
		}
		otherMove = other; // for TFT
	};

}