Elo rating simulation

elosim.js

/*********************************
*
* Elo Rating Simulation
*   Copyright (c) 2013, Max Irwin
*   MIT License
*
*********************************/

(function(){
	var players = [];
	
	var names = 'pawn,knight,bishop,rook,queen,king'.split(',');
	var skills = 'dead,weak,lame,student,bold,artful,strong,master'.split(',');
	
	//------------------------------------------------------------------	
	//Random number helpers
	var rand1 = function(max){ return Math.floor(Math.random()*max); }
	var rand2 = function(min,max){ return Math.floor(Math.random() * (max - min + 1)) + min; }
	
	//------------------------------------------------------------------
	//elo Rating calculation
	var elo = function (whiteRating,blackRating,whiteResult,blackResult,kwhite,kblack) {
		var expected = function(a,b) { return (1/(1+(Math.pow(10,(a-b)/400)))) };
		return {
			white: (whiteRating+(kwhite*(whiteResult-expected(blackRating,whiteRating)))),
			black: (blackRating+(kblack*(blackResult-expected(whiteRating,blackRating))))
		}
	}
	
	//------------------------------------------------------------------	
	//Plays and rates one game
	var game = function(white,black) {
		
		white.games++;black.games++;
	
		var chance;
		var whiteresult,blackresult;
		var wchance = rand1(white.skill);
		var bchance = rand1(black.skill);
	
		if (white.skill===black.skill) {
			chance = rand1(2)-1;
		} else if (wchance===bchance) {
			chance = 0;
		} else if (wchance<bchance) {
			chance = 1;
		} else {
			chance = -1;
		}
	
		switch (chance) {
			case -1: whiteresult=1;   blackresult=0;   white.won++;   black.lost++;  break;
			case 1: whiteresult=0;   blackresult=1;   white.lost++;  black.won++;   break;
			case 0: whiteresult=0.5; blackresult=0.5; white.drawn++; black.drawn++; break;
		}
	
		var kwhite = (white.games<400)?400:150;  
		var kblack = (black.games<400)?400:150;
		var ratings = elo(white.rating,black.rating,whiteresult,blackresult,kwhite,kblack);
		white.rating = ratings.white;
		black.rating = ratings.black;
	
	}
	
	//------------------------------------------------------------------	
	//Initialize players
	var init = function(){
	
		var player = function(name,skill){
			var self = this;
			self.name = 'The ' + skills[skill] + ' ' + names[name];
			self.skill = name+skill+1;
			//self.rating = 1000+rand1(skill*200);
			self.rating = 1400;
			self.games = 0;
			self.won = 0;
			self.lost = 0;
			self.drawn = 0;
		}
		
		player.prototype.toString = function() {
			var self = this;
			var pct = function(a,b) { return Math.floor(a/b*100) + '%'; }
			return [self.name+(self.name.length<16?'\t':''),Math.floor(self.rating),self.games,pct(self.won,self.games),pct(self.lost,self.games),pct(self.drawn,self.games)].join('\t\t');
		}
		
		for(var n=0,nl=names.length;n<nl;n++) {
			for(var s=0,sl=skills.length;s<sl;s++) {
				players.push(new player(n,s));
			}
		}
	
	}
	
	
	//------------------------------------------------------------------	
	//Run simulation:
	var simulate = function() {
		for(var i=0,l=players.length;i<1000000;i++) {
			var p1 = rand1(l),p2 = rand1(l);
			if (p1===p2) p2=p2?p2-1:1; //A player cannot play himself
			game(players[p1],players[p2]);
		}
	}
	
	//------------------------------------------------------------------	
	//Output results:
	var output = function() {
		players.sort(function(a,b) {return a.rating>b.rating?-1:1;}).map(function(player){console.log(player.toString())})
	};
	
	//==================================================================
	//Do It!
	init();
	simulate();
	output();
})();