add p_win method and misc cleanup and refactoring

* change g2rating,etc. to attr_reader (instead of attr_accessor)
* move @dvolatility into DVOL constant
* add p_win
* make comparison operator use p_win(self,other)
* use << when adding to results array instead of .push()
* improved comments; mostly from Glicko2 document
* minor variable renaming to improve readability
* clear results array after ratings are finally updated (no functional change, just cleaner)

cpp/glicko2.cpp

@@ -33,33 +33,33 @@
 
 class Glicko2_impl
 {
-public:
+	public:
 
-	// constructors
+		// constructors
-	Glicko2_impl();
+		Glicko2_impl();
-	Glicko2_impl(const Glicko2_impl& rhs);
+		Glicko2_impl(const Glicko2_impl& rhs);
 
-	// copy assignment
+		// copy assignment
-	Glicko2_impl& operator=(const Glicko2_impl& rhs);
+		Glicko2_impl& operator=(const Glicko2_impl& rhs);
 
-	// destructor
+		// destructor
-	virtual ~Glicko2_impl();
+		virtual ~Glicko2_impl();
 
-	// system constants
+		// system constants
-	static const double dvolatility;
+		static const double dvolatility;
 
-	// rating data
+		// rating data
-	double rating;
+		double rating;
-	double deviation;
+		double deviation;
-	double volatility;
+		double volatility;
 
-	// result data (copy of each opponent and results, 0.0, 0.5, or 1.0)
+		// result data (copy of each opponent and results, 0.0, 0.5, or 1.0)
-	std::vector<Glicko2> opponents;
+		std::vector<Glicko2> opponents;
-	std::vector<double>  results;
+		std::vector<double>  results;
 
-	// utility functions
+		// utility functions
-	double g(const double& deviation);
+		double g(const double& deviation);
-	double E(const double& rating, const double& rating_opponent, const double& deviation_opponent);
+		double E(const double& rating, const double& rating_opponent, const double& deviation_opponent);
 };
 
 
@@ -116,7 +116,7 @@ Glicko2_impl::~Glicko2_impl()
 
 double Glicko2_impl::g(const double& deviation)
 {
-	#define PI_SQUARED (9.86960440108935861883)
+#define PI_SQUARED (9.86960440108935861883)
 	return 1.0 / (sqrt(1.0 + 3.0 * deviation * deviation / PI_SQUARED));
 }
 

cpp/glicko2.h

@@ -47,195 +47,195 @@ class Glicko2_impl;
  */
 class Glicko2
 {
-public:
+	public:
 
 
 
-	/**
-	 * Enumeration of possible results.
-	 */
-	enum RESULT
-	{
-		/**
-		 * A win result, internally 1.0.
-		 */
-		WIN,
-
 		/**
-		 * A loss result, internally 0.0.
+		 * Enumeration of possible results.
 		 */
-		LOSS,
+		enum RESULT
+		{
+			/**
+			 * A win result, internally 1.0.
+			 */
+			WIN,
+
+			/**
+			 * A loss result, internally 0.0.
+			 */
+			LOSS,
+
+			/**
+			 * A draw result, internally 0.5.
+			 */
+			DRAW
+		};
+
+
 
 		/**
-		 * A draw result, internally 0.5.
+		 * Default constructor.  Initializes to a rating of 1500, a rating deviation 
+		 * of 350, and a volatility of 0.06.
 		 */
-		DRAW
+		Glicko2();
-	};
+
+		/**
+		 * Copy constructor.
+		 * 
+		 * @param rhs    Object to copy.
+		 */
+		Glicko2(const Glicko2& rhs);
+
+		/**
+		 * Constructor with rating, rating deviation, and volatility specified.
+		 * 
+		 * @param rating     Initial rating.
+		 * @param deviation  Initial rating deviation.
+		 * @param volatility Initial volatility.
+		 */
+		Glicko2(double rating, double deviation, double volatility);
 
 
 
-	/**
+		/**
-	 * Default constructor.  Initializes to a rating of 1500, a rating deviation 
+		 * Copy assignment operator.
-	 * of 350, and a volatility of 0.06.
+		 * 
-	 */
+		 * @param rhs    Object to copy.
-	Glicko2();
+		 * 
-
+		 * @return Reference to self after copy assignment.
-	/**
+		 */
-	 * Copy constructor.
+		Glicko2& operator=(const Glicko2& rhs);
-	 * 
-	 * @param rhs    Object to copy.
-	 */
-	Glicko2(const Glicko2& rhs);
-
-	/**
-	 * Constructor with rating, rating deviation, and volatility specified.
-	 * 
-	 * @param rating     Initial rating.
-	 * @param deviation  Initial rating deviation.
-	 * @param volatility Initial volatility.
-	 */
-	Glicko2(double rating, double deviation, double volatility);
 
 
 
-	/**
+		/**
-	 * Copy assignment operator.
+		 * Destructor.
-	 * 
+		 */
-	 * @param rhs    Object to copy.
+		virtual ~Glicko2();
-	 * 
-	 * @return Reference to self after copy assignment.
-	 */
-	Glicko2& operator=(const Glicko2& rhs);
 
 
 
-	/**
+		/**
-	 * Destructor.
+		 * Less than comparison operator.
-	 */
+		 * 
-	virtual ~Glicko2();
+		 * @param rhs   Object to compare against.
+		 * 
+		 * @return true if this object's rating is less than rhs's rating; false otherwise.
+		 */
+		bool operator< (const Glicko2& rhs);
 
 
 
-	/**
+		/**
-	 * Less than comparison operator.
+		 * Get the current rating. This rating is a Glicko rating, not a Glicko2 rating.
-	 * 
+		 * For details, please see http://www.glicko.com/
-	 * @param rhs    Object to compare against.
+		 * 
-	 * 
+		 * @return 
-	 * @return true if this object's rating is less than rhs's rating; false otherwise.
+		 */
-	 */
+		double GetRating() const;
-	bool operator< (const Glicko2& rhs);
+
+		/**
+		 * Get the current rating deviation. This is a Glicko rating deviation, not a 
+		 * Glicko-2 RD.  For details, please see http://www.glicko.com/
+		 * 
+		 * @return 
+		 */
+		double GetDeviation() const;
+
+		/**
+		 * Get the current rating volatility.
+		 * 
+		 * @return 
+		 */
+		double GetVolatility() const;
 
 
 
-	/**
+		/**
-	 * Get the current rating.  This rating is a Glicko rating, not a Glicko2 rating.
+		 * Set Glicko rating.  Internally this is converted to a Glicko2 rating.
-	 * For details, please see http://www.glicko.com/
+		 * For details, please see http://www.glicko.com/
-	 * 
+		 * 
-	 * @return 
+		 * @param rating Rating.
-	 */
+		 */
-	double GetRating() const;
+		void SetRating(double rating);
 
-	/**
+		/**
-	 * Get the current rating deviation.  This is a Glicko rating deviation, not a 
+		 * Set Glicko rating deviation.  Internally this is converted to a Glicko-2 RD.
-	 * Glicko-2 RD.  For details, please see http://www.glicko.com/
+		 * For details, please see http://www.glicko.com/
-	 * 
+		 * 
-	 * @return 
+		 * @param deviation Rating deviation.
-	 */
+		 */
-	double GetDeviation() const;
+		void SetDeviation(double deviation);
 
-	/**
+		/**
-	 * Get the current rating volatility.
+		 * Set rating volatility.
-	 * 
+		 * 
-	 * @return 
+		 * @param volatility Rating volatility.
-	 */
+		 */
-	double GetVolatility() const;
+		void SetVolatility(double volatility);
 
 
 
-	/**
+		/**
-	 * Set Glicko rating.  Internally this is converted to a Glicko2 rating.
+		 * Clear all results previously added via AddResult(), AddWin(), AddLoss(),
-	 * For details, please see http://www.glicko.com/
+		 * and/or AddDraw(). This method is called automatically whenever Update()
-	 * 
+		 * is called.
-	 * @param rating Rating.
+		 */
-	 */
+		void ClearResults();
-	void SetRating(double rating);
-
-	/**
-	 * Set Glicko rating deviation.  Internally this is converted to a Glicko-2 RD.
-	 * For details, please see http://www.glicko.com/
-	 * 
-	 * @param deviation Rating deviation.
-	 */
-	void SetDeviation(double deviation);
-
-	/**
-	 * Set rating volatility.
-	 * 
-	 * @param volatility Rating volatility.
-	 */
-	void SetVolatility(double volatility);
 
 
 
-	/**
+		/**
-	 * Clear all results previously added via AddResult(), AddWin(), AddLoss(),
+		 * Add a result to this rating.  Note that no calculation is performed until
-	 * and/or AddDraw().  This method is called automatically whenever Update()
+		 * Update() is called.
-	 * is called.
+		 * 
-	 */
+		 * @param opponent Other player in contest.
-	void ClearResults();
+		 * @param result   WIN, LOSS, or DRAW; from the point of view of this player.
+		 */
+		void AddResult(const Glicko2& opponent, RESULT result);
 
 
 
-	/**
+		/**
-	 * Add a result to this rating.  Note that no calculation is performed until
+		 * Add a win result to this rating.  Note that no calculation is performed until
-	 * Update() is called.
+		 * Update() is called.
-	 * 
+		 * 
-	 * @param opponent Other player in contest.
+		 * @param opponent Other (losing) player in contest.
-	 * @param result   WIN, LOSS, or DRAW; from the point of view of this player.
+		 */
-	 */
+		void AddWin(const Glicko2& opponent);
-	void AddResult(const Glicko2& opponent, RESULT result);
+
+		/**
+		 * Add a loss result to this rating. Note that no calculation is performed until
+		 * Update() is called.
+		 * 
+		 * @param opponent Other (winning) player in contest.
+		 */
+		void AddLoss(const Glicko2& opponent);
+
+		/**
+		 * Add a draw result to this rating. Note that no calculation is performed until
+		 * Update() is called.
+		 * 
+		 * @param opponent Other (drawing) player in contest.
+		 */
+		void AddDraw(const Glicko2& opponent);
 
 
 
-	/**
+		/**
-	 * Add a win result to this rating.  Note that no calculation is performed until
+		 * Update rating based on current results list, and clear results.
-	 * Update() is called.
+		 */
-	 * 
+		void Update();
-	 * @param opponent Other (losing) player in contest.
-	 */
-	void AddWin(const Glicko2& opponent);
-
-	/**
-	 * Add a loss result to this rating.  Note that no calculation is performed until
-	 * Update() is called.
-	 * 
-	 * @param opponent Other (winning) player in contest.
-	 */
-	void AddLoss(const Glicko2& opponent);
-
-	/**
-	 * Add a draw result to this rating.  Note that no calculation is performed until
-	 * Update() is called.
-	 * 
-	 * @param opponent Other (drawing) player in contest.
-	 */
-	void AddDraw(const Glicko2& opponent);
 
 
 
-	/**
+	private:
-	 * Update rating based on current results list, and clear results.
-	 */
-	void Update();
 
-
+		/**
-
+		 * Private Implementation.
-private:
+		 */
-
+		Glicko2_impl* pimpl;
-	/**
-	 * Private Implementation.
-	 */
-	Glicko2_impl* pimpl;
 
 };
 

py/glicko2.py

@@ -30,14 +30,14 @@ import copy
 class Glicko2:
     """
     Glicko-2 Rating calculator class.
-    
+
     This class implements the Glicko-2 rating system algorithm written by 
     Professor Mark E. Glickman.  All rating inputs and outputs are Glicko ratings,
     but internally everything is converted to and considered Glicko-2 ratings.
-    
+
     Glicko-2 is an improvement on the original Glicko, which was, in turn, an
     improvement on the ELO system.
-    
+
     The Glicko-2 system is specified on http://www.glicko.com/
     """
 
@@ -229,12 +229,12 @@ if __name__ == "__main__":
     B = Glicko2(1400.0,  30.0, 0.06)
     C = Glicko2(1550.0, 100.0, 0.06)
     D = Glicko2(1700.0, 300.0, 0.06)
-    
+
     A.AddWin(B)
     A.AddLoss(C)
     A.AddResult(D,Glicko2.LOSS)
-    
+
     A.Update();
-    
+
     print "rating",A.GetRating(), "deviation",A.GetDeviation()
 

rb/glicko2.rb

@@ -1,4 +1,4 @@
-#!/usr/bin/env ruby
+#!/usr/bin/env ruby -w
 
 #
 #
@@ -38,179 +38,187 @@
 # 
 class Glicko2
 
-	protected
+  protected
 
-		# Glicko2 reprensentation (Glicko2 uses different scales from Glicko)
+  # Glicko2 reprensentation (Glicko2 uses different scales from Glicko)
-		attr_accessor :g2rating, :g2deviation, :g2volatility
+  attr_reader :g2rating, :g2deviation, :g2volatility
-	
-		# a nested Class to hold a single result
-		Result = Struct.new(:opponent, :result)
 
-	public
+  # a nested Class to hold a single result
+  Result = Struct.new(:opponent, :result)
 
-		WIN  = 1.0
+  public
-		LOSS = 0.0
-		DRAW = 0.5
-		
-		# Constructor with rating, rating deviation, and volatility optionally
-		# specified.  If nothing specified, nitializes to a rating of 1500, a 
-		# rating deviation of 350, and a volatility of 0.06.
-		def initialize(rating = 1500.0, deviation = 350.0, volatility = 0.06)
-			@dvolatility    = 0.3
-			self.rating     = rating
-			self.deviation  = deviation
-			self.volatility = volatility
-			clear_results
-		end
 
-		include Comparable
+  WIN  = 1.0
+  LOSS = 0.0
+  DRAW = 0.5
 
-		# Comparison operator
+  # system constant, determines delta volatility over time; should be [0.3,1.2]
-		def <=>(other)
+  DVOL = 0.3
-			self.rating <=> other.rating
-		end
 
-		# Get the current rating.  This rating is a Glicko rating, not a Glicko2 rating.
+  # Constructor with rating, rating deviation, and volatility optionally
-		# For details, please see http://www.glicko.com/
+  # specified.  If nothing specified, nitializes to a rating of 1500, a 
-		def rating
+  # rating deviation of 350, and a volatility of 0.06.
-			(@g2rating * 173.7178) + 1500.0
+  def initialize(rating = 1500.0, deviation = 350.0, volatility = 0.06)
-		end
+    self.rating     = rating
+    self.deviation  = deviation
+    self.volatility = volatility
+    clear_results
+  end
 
-		# Set Glicko rating.  Internally this is converted to a Glicko2 rating.
+  include Comparable
-		# For details, please see http://www.glicko.com/
-		def rating=(r)
-			@g2rating = (r - 1500.0) / 173.7178
-		end
 
-		# Get the current rating deviation.  This is a Glicko rating deviation, not a 
+  # Comparison operator
-		# Glicko-2 RD.  For details, please see http://www.glicko.com/
+  def <=>(other)
-		def deviation
+    p_win(other) <=> 0.5
-			@g2deviation * 173.7178
+  end
-		end
 
-		# Set Glicko rating deviation.  Internally this is converted to a Glicko-2 RD.
+  # get the probability of beating opponent
-		# For details, please see http://www.glicko.com/
+  def p_win(opponent)
-		def deviation=(d)
+    1.0 / (1.0 + 10.0**(((opponent.rating - self.rating) / (400.0 * Math.sqrt(1.0 + 0.0000100723986 * (self.deviation**2.0 + opponent.deviation**2.0))))))
-			@g2deviation = d / 173.7178
+  end
-		end
 
-		# Get the current rating volatility.
+  # Get the current rating.  This rating is a Glicko rating, not a Glicko2 rating.
-		def volatility
+  # For details, please see http://www.glicko.com/
-			@g2volatility
+  def rating
-		end
+    (@g2rating * 173.7178) + 1500.0
+  end
 
-		# Set rating volatility.
+  # Set Glicko rating.  Internally this is converted to a Glicko2 rating.
-		def volatility=(v)
+  # For details, please see http://www.glicko.com/
-			@g2volatility = v
+  def rating=(r)
-		end
+    @g2rating = (r - 1500.0) / 173.7178
+  end
 
-		# Clear all results previously added via add_result(), add_win(), add_loss(),
+  # Get the current rating deviation.  This is a Glicko rating deviation, not a 
-		# and/or add_draw().  This method is called automatically whenever update()
+  # Glicko-2 RD.  For details, please see http://www.glicko.com/
-		# is called.
+  def deviation
-		def clear_results
+    @g2deviation * 173.7178
-			@opponents = []
+  end
-			@results = []
-		end
 
-		# Add a result to this rating.  Note that no calculation is performed until
+  # Set Glicko rating deviation.  Internally this is converted to a Glicko-2 RD.
-		# update() is called.
+  # For details, please see http://www.glicko.com/
-		def add_result(opponent,result)
+  def deviation=(d)
-			@results.push( Result.new(opponent.clone, result) )
+    @g2deviation = d / 173.7178
-		end
+  end
 
-		# Add a win result to this rating.  Note that no calculation is performed until
+  # Get the current rating volatility.
-		# update() is called.
+  def volatility
-		def add_win(opponent)
+    @g2volatility
-			add_result(opponent,Glicko2::WIN)
+  end
-		end
 
-		# Add a loss result to this rating.  Note that no calculation is performed until
+  # Set rating volatility.
-		# update() is called.
+  def volatility=(v)
-		def add_loss(opponent)
+    @g2volatility = v
-			add_result(opponent,Glicko2::LOSS)
+  end
-		end
 
-		# Add a draw result to this rating.  Note that no calculation is performed until
+  # Clear all results previously added via add_result(), add_win(), add_loss(),
-		# update() is called.
+  # and/or add_draw().  This method is called automatically whenever update()
-		def add_draw(opponent)
+  # is called.
-			add_result(opponent,Glicko2::DRAW)
+  def clear_results
-		end
+    @opponents = Array.new
-	
+    @results   = Array.new
-		# Update rating based on current results list, and clear results.
+  end
-		def update
-		
-			# util func
-			def Glicko2.g(deviation)
-				1.0 / (Math.sqrt(1.0 + 3.0 * deviation ** 2.0 / (Math::PI ** 2.0)))
-			end
-		
-			# util func
-			def Glicko2.E(rating, rating_opponent, deviation_opponent)
-				1.0 / (1.0 + Math.exp(-Glicko2.g(deviation_opponent)*(rating - rating_opponent)));
-			end
-		
-			# bail if no opponents set
-			if @results.empty?
-				return nil
-			end
 
-			# compute variance
+  # Add a result to this rating.  Note that no calculation is performed until
+  # update() is called.
+  def add_result(opponent,result)
+    @results << Result.new(opponent.clone, result)
+  end
 
-			#variance = 0.0
+  # Add a win result to this rating.  Note that no calculation is performed until
-			#@results.inject(0.0) do |variance,r|
+  # update() is called.
-			#	g_i = Glicko2.g(r.opponent.g2deviation)
+  def add_win(opponent)
-			#	e_i = Glicko2.E(@g2rating,r.opponent.g2rating,r.opponent.g2deviation)
+    add_result(opponent,Glicko2::WIN)
-			#	g_i ** 2.0 * e_i * (1.0 - e_i)
+  end
-			#end
 
-			variance = 0.0
+  # Add a loss result to this rating.  Note that no calculation is performed until
-			@results.each do |r|
+  # update() is called.
-				g_i = Glicko2.g(r.opponent.g2deviation)
+  def add_loss(opponent)
-				e_i = Glicko2.E(@g2rating,r.opponent.g2rating,r.opponent.g2deviation)
+    add_result(opponent,Glicko2::LOSS)
-				variance += g_i ** 2.0 * e_i * (1.0 - e_i)
+  end
-			end
-			variance = 1.0 / variance
-		
-			# compute delta
-			delta = 0.0
-			@results.each do |r|
-				delta += Glicko2.g(r.opponent.g2deviation) * (r.result - Glicko2.E(@g2rating, r.opponent.g2rating, r.opponent.g2deviation))
-			end
-			delta *= variance
-		
-			# determine new volatility
-			new_volatility = 0.0
-			a              = Math.log( @g2volatility**2.0 )
-			x              = 0.0
-			x_new          = a
-			while ( (x - x_new).abs > 0.0000001 )
-				x     = x_new
-				d     = @g2deviation**2.0 + variance + Math.exp(x)
-				h1    = -(x - a)/(@dvolatility**2.0) - 0.5*Math.exp(x)/d + 0.5*Math.exp(x)*(delta/d)*(delta/d)
-				h2    = -1.0/(@dvolatility**2.0) - 0.5*Math.exp(x)*(@g2deviation**2.0+variance)/(d**2.0) + 0.5*(delta**2.0)*Math.exp(x)*((@g2deviation**2.0) + variance - Math.exp(x))/(d**3.0)
-				x_new = x - h1/h2
-			end
-			new_volatility = Math.exp(x_new / 2.0)
-		
-			# update the rating deviation to the new pre-rating period value
-			pre_deviation = Math.sqrt( @g2deviation**2.0 + new_volatility**2.0 )
 
-			# update the rating and deviation
+  # Add a draw result to this rating.  Note that no calculation is performed until
-			new_deviation = 1.0 / (Math.sqrt( 1.0/(pre_deviation**2.0) + 1.0 / variance))
+  # update() is called.
-			new_rating    = 0.0
+  def add_draw(opponent)
-			@results.each do |r|
+    add_result(opponent,Glicko2::DRAW)
-			    new_rating += Glicko2.g(r.opponent.g2deviation) * (r.result - Glicko2.E(@g2rating, r.opponent.g2rating, r.opponent.g2deviation))
+  end
-			end
-			new_rating  = new_rating * new_deviation**2.0
-			new_rating += @g2rating
 
-			# wipe our result lists
+  # util func 'g'
-			clear_results
+  def Glicko2.g(deviation)
+    1.0 / (Math.sqrt(1.0 + 3.0 * deviation ** 2.0 / (Math::PI ** 2.0)))
+  end
+
+  # util func 'E'
+  def Glicko2.E(rating, rating_opponent, deviation_opponent)
+    1.0 / (1.0 + Math.exp(-Glicko2.g(deviation_opponent)*(rating - rating_opponent)));
+  end
+
+  # Update rating based on current results list, and clear results.
+  def update
+    # Note that if a player does not compete during the rating period, then
+    # only Step 6 applies. 
+    if @results.empty?
+      # In this case, the player's rating and volatility parameters remain the
+      # same, but the RD increases according to:
+      @g2deviation = Math.sqrt(@g2deviation**2.0 + @g2volatility**2.0)
+      return
+    end
+
+    # Step 1. Determine a rating and RD for each player at the onset of the
+    # rating period. The system constant which constrains the change in
+    # volatility over time, needs to be set prior to application of the system.
+    # Reasonable choices are between 0.3 and 1.2, though the system should be
+    # tested to decide which value results in greatest predictive accuracy
+    # ... (ratings already stored in instance)
+
+    # Step 2. For each player, convert the ratings and RD's onto the Glicko-2
+    # scale.
+    # ... (ratings already stored in G2 format)
+
+    # Step 3.  Compute the quantity v. This is the estimated variance of the
+    # team's/player's rating based only on game outcomes.
+    variance = 1.0 / @results.inject(0.0) do |sum,r|
+      g_i = Glicko2.g(r.opponent.g2deviation)
+      e_i = Glicko2.E(@g2rating, r.opponent.g2rating, r.opponent.g2deviation)
+      sum + g_i**2.0 * e_i * (1.0 - e_i)
+    end
+
+    # Step 4. Compute the quantity delta, the estimated improvement in rating
+    # by comparing the pre-period rating to the performance rating based only
+    # on game outcomes.
+    delta = variance * @results.inject(0.0) do |sum,r|
+      sum + Glicko2.g(r.opponent.g2deviation) * (r.result - Glicko2.E(@g2rating, r.opponent.g2rating, r.opponent.g2deviation))
+    end
+
+    # Step 5. Determine the new value of the volatility.
+    a     = Math.log(@g2volatility**2.0)
+    x0, x = 0.0, a
+    while ((x0 - x).abs > 0.0000001)
+      x0 = x
+      d  = @g2deviation**2.0 + variance + Math.exp(x0)
+      h1 = -(x0 - a)/(DVOL**2.0) - 0.5*Math.exp(x0)/d + 0.5*Math.exp(x0)*(delta/d)*(delta/d)
+      h2 = -1.0/(DVOL**2.0) - 0.5*Math.exp(x0)*(@g2deviation**2.0+variance)/(d**2.0) + 0.5*(delta**2.0)*Math.exp(x0)*((@g2deviation**2.0) + variance - Math.exp(x0))/(d**3.0)
+      x  = x0 - h1/h2
+    end
+    new_volatility = Math.exp(x / 2.0)
+
+    # Step 6. Update the rating deviation to the new pre-rating period value.
+    pre_deviation = Math.sqrt(@g2deviation**2.0 + new_volatility**2.0)
+
+    # Step 7. Update the rating and RD to the new values.
+    new_deviation = 1.0 / (Math.sqrt(1.0/(pre_deviation**2.0) + 1.0 / variance))
+    new_rating    = @g2rating + new_deviation**2.0 * @results.inject(0.0) do |sum,r|
+      sum + Glicko2.g(r.opponent.g2deviation) * (r.result - Glicko2.E(@g2rating, r.opponent.g2rating, r.opponent.g2deviation))
+    end
+
+    # Step 8. Convert ratings and RD's back to original scale.
+    @g2deviation  = new_deviation
+    @g2volatility = new_volatility
+    @g2rating     = new_rating
+
+    # wipe our result lists
+    clear_results
+  end
 
-			# copy new values
-			@g2deviation  = new_deviation
-			@g2volatility = new_volatility
-			@g2rating     = new_rating
-		end
 end
 

rb/test_glicko2.rb

@@ -1,34 +1,34 @@
-#!/usr/bin/env ruby
+#!/usr/bin/env ruby -w
 
-require 'glicko2'
+require_relative 'glicko2'
 require 'test/unit'
 
 class TestGlicko2 < Test::Unit::TestCase
 
-	def test_simple
+  def test_simple
-		a = Glicko2.new(1500.0, 200.0, 0.06)
+    a = Glicko2.new(1500.0, 200.0, 0.06)
-		b = Glicko2.new(1400.0,  30.0, 0.06)
+    b = Glicko2.new(1400.0,  30.0, 0.06)
-		c = Glicko2.new(1550.0, 100.0, 0.06)
+    c = Glicko2.new(1550.0, 100.0, 0.06)
-		d = Glicko2.new(1700.0, 300.0, 0.06)
+    d = Glicko2.new(1700.0, 300.0, 0.06)
-		
-		a.add_win(b)
-		a.add_loss(c)
-		a.add_result(d,0.0)
-		
-		assert_equal(1500.0, a.rating)
-		assert_equal(200.0, a.deviation)
-		
-		a.update()
-		
-		assert_in_delta(1464.05,a.rating,0.01)
-		assert_in_delta(151.516,a.deviation,0.01)
 
-		a.update()
+    a.add_win(b)
-		
+    a.add_loss(c)
-		assert_in_delta(1464.05,a.rating,0.01)
+    a.add_result(d,0.0)
-		assert_in_delta(151.516,a.deviation,0.01)
+
+    assert_equal(1500.0, a.rating)
+    assert_equal(200.0, a.deviation)
+
+    a.update()
+
+    assert_in_delta(1464.05,a.rating,0.01)
+    assert_in_delta(151.516,a.deviation,0.01)
+
+    a.update()
+
+    assert_in_delta(1464.05,a.rating,0.01)
+    assert_in_delta(151.875,a.deviation,0.01)
+
+  end
 
-	end
-	
 end