Merge pull request #8279 from ddugovic/rating-advantage

Ratings - account for first player advantage #6818
lichess-org · Mar 2, 2021 · 725704c · 725704c
2 parents e09edd4 + 4136df6
commit 725704c
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Showing 3 changed files with 41 additions and 12 deletions.
diff --git a/modules/rating/src/main/java/glicko2/Rating.java b/modules/rating/src/main/java/glicko2/Rating.java
@@ -19,6 +19,7 @@
  */
 public class Rating {
 
+	private final double advantage;
 	private double rating;
 	private double ratingDeviation;
 	private double volatility;
@@ -31,17 +32,35 @@ public class Rating {
 	private double workingVolatility;
 
 	public Rating(double initRating, double initRatingDeviation, double initVolatility, int nbResults) {
-		this(initRating, initRatingDeviation, initVolatility, nbResults, null);
+		this(0.0d, initRating, initRatingDeviation, initVolatility, nbResults, null);
 	}
 
 	public Rating(double initRating, double initRatingDeviation, double initVolatility, int nbResults, DateTime lastRatingPeriodEndDate) {
+		this(0.0d, initRating, initRatingDeviation, initVolatility, nbResults, lastRatingPeriodEndDate);
+	}
+
+	public Rating(double advantage, double initRating, double initRatingDeviation, double initVolatility, int nbResults, DateTime lastRatingPeriodEndDate) {
+		this.advantage = advantage;
 		this.rating = initRating;
 		this.ratingDeviation = initRatingDeviation;
 		this.volatility = initVolatility;
 		this.numberOfResults = nbResults;
 		this.lastRatingPeriodEndDate = lastRatingPeriodEndDate;
 	}
 
+	public Rating withAdvantage(double advantage) {
+        return new Rating(advantage, rating, ratingDeviation, volatility, numberOfResults, lastRatingPeriodEndDate);
+	}
+
+	/**
+	 * Return the skill advantage (first-player handicap) value.
+	 *
+	 * @return double
+	 */
+	public double getAdvantage() {
+		return this.advantage;
+	}
+
 	/**
 	 * Return the average skill value of the player.
 	 *
@@ -55,6 +74,16 @@ public void setRating(double rating) {
 		this.rating = rating;
 	}
 
+	/**
+	 * Return the average skill value of the player scaled down
+	 * to the scale used by the algorithm's internal workings.
+	 *
+	 * @return double
+	 */
+	public double getGlicko2RatingWithAdvantage() {
+		return RatingCalculator.convertRatingToGlicko2Scale(this.rating + advantage);
+	}
+
 	/**
 	 * Return the average skill value of the player scaled down
 	 * to the scale used by the algorithm's internal workings.
@@ -70,7 +99,7 @@ public double getGlicko2Rating() {
 	 *
 	 * @param double
 	 */
-	public void setGlicko2Rating(double rating) {
+	private void setGlicko2Rating(double rating) {
 		this.rating = RatingCalculator.convertRatingToOriginalGlickoScale(rating);
 	}
 

diff --git a/modules/rating/src/main/java/glicko2/RatingCalculator.java b/modules/rating/src/main/java/glicko2/RatingCalculator.java
@@ -25,7 +25,7 @@ public class RatingCalculator {
   private final static double DEFAULT_TAU =  0.75;
   private final static double MULTIPLIER =  173.7178;
   private final static double CONVERGENCE_TOLERANCE =  0.000001;
-  private final static int ITERATION_MAX =  3000;
+  private final static int ITERATION_MAX =  1000;
   private final static double DAYS_PER_MILLI =  1.0 / (1000 * 60 * 60 * 24);
 
   private final double tau; // constrains volatility over time
@@ -254,11 +254,11 @@ private double v(Rating player, List<Result> results) {
     for ( Result result: results ) {
       v = v + (
           ( Math.pow( g(result.getOpponent(player).getGlicko2RatingDeviation()), 2) )
-          * E(player.getGlicko2Rating(),
-            result.getOpponent(player).getGlicko2Rating(),
+          * E(player.getGlicko2RatingWithAdvantage(),
+            result.getOpponent(player).getGlicko2RatingWithAdvantage(),
             result.getOpponent(player).getGlicko2RatingDeviation())
-          * ( 1.0 - E(player.getGlicko2Rating(),
-              result.getOpponent(player).getGlicko2Rating(),
+          * ( 1.0 - E(player.getGlicko2RatingWithAdvantage(),
+              result.getOpponent(player).getGlicko2RatingWithAdvantage(),
               result.getOpponent(player).getGlicko2RatingDeviation())
             ));
     }
@@ -293,8 +293,8 @@ private double outcomeBasedRating(Rating player, List<Result> results) {
       outcomeBasedRating = outcomeBasedRating
         + ( g(result.getOpponent(player).getGlicko2RatingDeviation())
             * ( result.getScore(player) - E(
-                player.getGlicko2Rating(),
-                result.getOpponent(player).getGlicko2Rating(),
+                player.getGlicko2RatingWithAdvantage(),
+                result.getOpponent(player).getGlicko2RatingWithAdvantage(),
                 result.getOpponent(player).getGlicko2RatingDeviation() ))
           );
     }

diff --git a/modules/round/src/main/PerfsUpdater.scala b/modules/round/src/main/PerfsUpdater.scala
@@ -124,9 +124,9 @@ final class PerfsUpdater(
   private def updateRatings(white: Rating, black: Rating, result: Glicko.Result): Unit = {
     val results = new RatingPeriodResults()
     result match {
-      case Glicko.Result.Draw => results.addDraw(white, black)
-      case Glicko.Result.Win  => results.addResult(white, black)
-      case Glicko.Result.Loss => results.addResult(black, white)
+      case Glicko.Result.Draw => results.addDraw(white.withAdvantage(5), black.withAdvantage(-5))
+      case Glicko.Result.Win  => results.addResult(white.withAdvantage(5), black.withAdvantage(-5))
+      case Glicko.Result.Loss => results.addResult(black.withAdvantage(-5), white.withAdvantage(5))
     }
     try {
       Glicko.system.updateRatings(results, true)