Rate games accounting for first move advantage (fix #6818)

modules/puzzle/src/main/PuzzleFinisher.scala

@@ -199,18 +199,16 @@ final private[puzzle] class PuzzleFinisher(
       if player.clueless then glicko._1
       else glicko._1.average(glicko._2, weightOf(angle, win))
 
-  private val VOLATILITY = lila.rating.Glicko.default.volatility
-  private val TAU        = 0.75d
-  private val calculator = glicko2.RatingCalculator(VOLATILITY, TAU)
+  private val calculator = lila.rating.Glicko.system
 
   def incPuzzlePlays(puzzleId: PuzzleId): Funit =
     colls.puzzle.map(_.incFieldUnchecked($id(puzzleId), Puzzle.BSONFields.plays))
 
   private def updateRatings(u1: glicko2.Rating, u2: glicko2.Rating, win: PuzzleWin): Unit =
-    val results = glicko2.GameRatingPeriodResults(
+    val results = glicko2.BinaryRatingPeriodResults(
       List(
-        if win.yes then glicko2.GameResult(u1, u2, false)
-        else glicko2.GameResult(u2, u1, false)
+        if win.yes then glicko2.BinaryResult(u1, u2, false)
+        else glicko2.BinaryResult(u2, u1, false)
       )
     )
     try calculator.updateRatings(results)

modules/rating/src/main/Glicko.scala

@@ -76,8 +76,9 @@ object Glicko:
   // rating that can be lost or gained with a single game
   val maxRatingDelta = 700
 
-  val tau    = 0.75d
-  val system = glicko2.RatingCalculator(tau, ratingPeriodsPerDay)
+  val tau                           = 0.75d
+  val system                        = glicko2.RatingCalculator(tau, ratingPeriodsPerDay)
+  def calculator(advantage: Double) = glicko2.RatingCalculator(advantage, tau, ratingPeriodsPerDay)
 
   def liveDeviation(p: Perf, reverse: Boolean): Double = {
     system.previewDeviation(p.toRating, nowInstant, reverse)

modules/rating/src/main/glicko2/Rating.scala

@@ -21,6 +21,10 @@ final class Rating(
     */
   def getGlicko2Rating: Double = convertRatingToGlicko2Scale(this.rating)
 
+  def getGlicko2RatingWithAdvantage(advantage: Double): Double = convertRatingToGlicko2Scale(
+    this.rating + advantage
+  )
+
   /** Set the average skill value, taking in a value in Glicko2 scale.
     */
   def setGlicko2Rating(r: Double) =

modules/rating/src/main/glicko2/RatingCalculator.scala

@@ -20,6 +20,7 @@ object RatingCalculator:
     (ratingDeviation / MULTIPLIER)
 
 final class RatingCalculator(
+    advantage: Double = 0.0d,
     tau: Double = 0.75d,
     ratingPeriodsPerDay: Double = 0
 ):
@@ -33,10 +34,9 @@ final class RatingCalculator(
 
   val ratingPeriodsPerMilli: Double = ratingPeriodsPerDay * DAYS_PER_MILLI
 
-  /** <p>Run through all players within a resultset and calculate their new ratings.</p> <p>Players within the
-    * resultset who did not compete during the rating period will have see their deviation increase (in line
-    * with Prof Glickman's paper).</p> <p>Note that this method will clear the results held in the association
-    * resultset.</p>
+  /** Run through all players within a resultset and calculate their new ratings. Players within the resultset
+    * who did not compete during the rating period will have see their deviation increase (in line with Prof
+    * Glickman's paper). Note that this method will clear the results held in the association resultset.
     *
     * @param results
     */
@@ -166,13 +166,13 @@ final class RatingCalculator(
     for result <- results do
       v = v + ((Math.pow(g(result.getOpponent(player).getGlicko2RatingDeviation), 2))
         * E(
-          player.getGlicko2Rating,
-          result.getOpponent(player).getGlicko2Rating,
+          player.getGlicko2RatingWithAdvantage(result.getAdvantage(advantage, player)),
+          result.getOpponent(player).getGlicko2RatingWithAdvantage(-result.getAdvantage(advantage, player)),
           result.getOpponent(player).getGlicko2RatingDeviation
         )
         * (1.0 - E(
-          player.getGlicko2Rating,
-          result.getOpponent(player).getGlicko2Rating,
+          player.getGlicko2RatingWithAdvantage(result.getAdvantage(advantage, player)),
+          result.getOpponent(player).getGlicko2RatingWithAdvantage(-result.getAdvantage(advantage, player)),
           result.getOpponent(player).getGlicko2RatingDeviation
         )))
     1 / v
@@ -193,8 +193,8 @@ final class RatingCalculator(
       outcomeBasedRating = outcomeBasedRating
         + (g(result.getOpponent(player).getGlicko2RatingDeviation)
           * (result.getScore(player) - E(
-            player.getGlicko2Rating,
-            result.getOpponent(player).getGlicko2Rating,
+            player.getGlicko2RatingWithAdvantage(result.getAdvantage(advantage, player)),
+            result.getOpponent(player).getGlicko2RatingWithAdvantage(-result.getAdvantage(advantage, player)),
             result.getOpponent(player).getGlicko2RatingDeviation
           )))
     outcomeBasedRating

modules/rating/src/main/glicko2/RatingPeriodResults.scala

@@ -8,5 +8,4 @@ trait RatingPeriodResults[R <: Result]():
 
 class GameRatingPeriodResults(val results: List[GameResult]) extends RatingPeriodResults[GameResult]
 
-class FloatingRatingPeriodResults(val results: List[FloatingResult])
-    extends RatingPeriodResults[FloatingResult]
+class BinaryRatingPeriodResults(val results: List[BinaryResult]) extends RatingPeriodResults[BinaryResult]

modules/rating/src/main/glicko2/Result.scala

@@ -2,6 +2,8 @@ package lila.rating.glicko2
 
 trait Result:
 
+  def getAdvantage(advantage: Double, player: Rating): Double
+
   def getScore(player: Rating): Double
 
   def getOpponent(player: Rating): Rating
@@ -10,42 +12,48 @@ trait Result:
 
   def players: List[Rating]
 
-// score from 0 (opponent wins) to 1 (player wins)
-class FloatingResult(player: Rating, opponent: Rating, score: Float) extends Result:
+class BinaryResult(first: Rating, second: Rating, score: Boolean) extends Result:
+  private val POINTS_FOR_WIN  = 1.0d
+  private val POINTS_FOR_LOSS = 0.0d
+
+  def getAdvantage(advantage: Double, p: Rating) = 0.0d
 
-  def getScore(p: Rating) = if p == player then score else 1 - score
+  def getScore(p: Rating) = if p == first then if score then POINTS_FOR_WIN else POINTS_FOR_LOSS
+  else if score then POINTS_FOR_LOSS
+  else POINTS_FOR_WIN
 
-  def getOpponent(p: Rating) = if p == player then opponent else player
+  def getOpponent(p: Rating) = if p == first then second else first
 
-  def participated(p: Rating) = p == player || p == opponent
+  def participated(p: Rating) = p == first || p == second
 
-  def players = List(player, opponent)
+  def players = List(first, second)
 
-final class GameResult(winner: Rating, loser: Rating, isDraw: Boolean) extends Result:
+final class GameResult(first: Rating, second: Rating, outcome: Option[Boolean]) extends Result:
   private val POINTS_FOR_WIN  = 1.0d
-  private val POINTS_FOR_LOSS = 0.0d
   private val POINTS_FOR_DRAW = 0.5d
+  private val POINTS_FOR_LOSS = 0.0d
 
-  def players = List(winner, loser)
+  def players = List(first, second)
 
-  def participated(player: Rating) = player == winner || player == loser
+  def participated(player: Rating) = player == first || player == second
+
+  def getAdvantage(advantage: Double, player: Rating) =
+    if player == first then advantage / 2.0d else -advantage / 2.0d
 
   /** Returns the "score" for a match.
     *
-    * @param player
     * @return
-    *   1 for a win, 0.5 for a draw and 0 for a loss
+    *   1 for a first player win, 0.5 for a draw and 0 for a first player loss
     * @throws IllegalArgumentException
     */
-  def getScore(player: Rating): Double =
-    if isDraw then POINTS_FOR_DRAW
-    else if winner == player then POINTS_FOR_WIN
-    else if loser == player then POINTS_FOR_LOSS
-    else throw new IllegalArgumentException("Player did not participate in match");
+  def getScore(player: Rating): Double = outcome match
+    case Some(true)  => if player == first then POINTS_FOR_WIN else POINTS_FOR_LOSS
+    case Some(false) => if player == first then POINTS_FOR_LOSS else POINTS_FOR_WIN
+    case _           => POINTS_FOR_DRAW
 
   def getOpponent(player: Rating) =
-    if winner == player then loser
-    else if loser == player then winner
+    if first == player then second
+    else if second == player then first
     else throw new IllegalArgumentException("Player did not participate in match");
 
-  override def toString = s"$winner vs $loser = $isDraw"
+  override def toString = s"$first vs $second = $outcome"

modules/rating/src/test/RatingCalculatorTest.scala

@@ -8,7 +8,6 @@ import lila.rating.PerfExt.*
 import glicko2.*
 
 class RatingCalculatorTest extends lila.common.LilaTest:
-
   def updateRatings(wRating: Rating, bRating: Rating, winner: Option[Color]) =
     val result = winner match
       case Some(chess.White) => Glicko.Result.Win
@@ -17,43 +16,43 @@ class RatingCalculatorTest extends lila.common.LilaTest:
     val results = GameRatingPeriodResults(
       List(
         result match
-          case Glicko.Result.Draw => GameResult(wRating, bRating, true)
-          case Glicko.Result.Win  => GameResult(wRating, bRating, false)
-          case Glicko.Result.Loss => GameResult(bRating, wRating, false)
+          case Glicko.Result.Win  => GameResult(wRating, bRating, Some(true))
+          case Glicko.Result.Loss => GameResult(wRating, bRating, Some(false))
+          case Glicko.Result.Draw => GameResult(wRating, bRating, None)
       )
     )
-    Glicko.system.updateRatings(results, true)
+    Glicko.calculator(35.0d).updateRatings(results, true)
 
   test("default deviation: white wins") {
     val wr = default.toRating
     val br = default.toRating
     updateRatings(wr, br, White.some)
-    assertCloseTo(wr.rating, 1741d, 1d)
-    assertCloseTo(br.rating, 1258d, 1d)
-    assertCloseTo(wr.ratingDeviation, 396d, 1d)
-    assertCloseTo(br.ratingDeviation, 396d, 1d)
-    assertCloseTo(wr.volatility, 0.0899983, 0.00000001d)
-    assertCloseTo(br.volatility, 0.0899983, 0.0000001d)
+    assertCloseTo(wr.rating, 1729d, 1d)
+    assertCloseTo(br.rating, 1271d, 1d)
+    assertCloseTo(wr.ratingDeviation, 396.9015d, 0.0001d)
+    assertCloseTo(br.ratingDeviation, 396.9015d, 0.0001d)
+    assertCloseTo(wr.volatility, 0.0899980, 0.0000001d)
+    assertCloseTo(br.volatility, 0.0899980, 0.0000001d)
   }
   test("default deviation: black wins") {
     val wr = default.toRating
     val br = default.toRating
     updateRatings(wr, br, Black.some)
-    assertCloseTo(wr.rating, 1258d, 1d)
-    assertCloseTo(br.rating, 1741d, 1d)
-    assertCloseTo(wr.ratingDeviation, 396d, 1d)
-    assertCloseTo(br.ratingDeviation, 396d, 1d)
-    assertCloseTo(wr.volatility, 0.0899983, 0.00000001d)
-    assertCloseTo(br.volatility, 0.0899983, 0.0000001d)
+    assertCloseTo(wr.rating, 1245d, 1d)
+    assertCloseTo(br.rating, 1755d, 1d)
+    assertCloseTo(wr.ratingDeviation, 396.9015d, 0.0001d)
+    assertCloseTo(br.ratingDeviation, 396.9015d, 0.0001d)
+    assertCloseTo(wr.volatility, 0.0899986, 0.0000001d)
+    assertCloseTo(br.volatility, 0.0899986, 0.0000001d)
   }
   test("default deviation: draw") {
     val wr = default.toRating
     val br = default.toRating
     updateRatings(wr, br, None)
-    assertCloseTo(wr.rating, 1500d, 1d)
-    assertCloseTo(br.rating, 1500d, 1d)
-    assertCloseTo(wr.ratingDeviation, 396d, 1d)
-    assertCloseTo(br.ratingDeviation, 396d, 1d)
+    assertCloseTo(wr.rating, 1487d, 1d)
+    assertCloseTo(br.rating, 1513d, 1d)
+    assertCloseTo(wr.ratingDeviation, 396.9015d, 0.0001d)
+    assertCloseTo(br.ratingDeviation, 396.9015d, 0.0001d)
     assertCloseTo(wr.volatility, 0.0899954, 0.0000001d)
     assertCloseTo(br.volatility, 0.0899954, 0.0000001d)
   }
@@ -67,32 +66,32 @@ class RatingCalculatorTest extends lila.common.LilaTest:
     val wr = perf.toRating
     val br = perf.toRating
     updateRatings(wr, br, White.some)
-    assertCloseTo(wr.rating, 1517d, 1d)
-    assertCloseTo(br.rating, 1482d, 1d)
-    assertCloseTo(wr.ratingDeviation, 78d, 1d)
-    assertCloseTo(br.ratingDeviation, 78d, 1d)
+    assertCloseTo(wr.rating, 1515d, 1d)
+    assertCloseTo(br.rating, 1485d, 1d)
+    assertCloseTo(wr.ratingDeviation, 78.0967d, 0.0001d)
+    assertCloseTo(br.ratingDeviation, 78.0967d, 0.0001d)
     assertCloseTo(wr.volatility, 0.06, 0.00001d)
     assertCloseTo(br.volatility, 0.06, 0.00001d)
   }
   test("low deviation: black wins") {
     val wr = perf.toRating
     val br = perf.toRating
     updateRatings(wr, br, Black.some)
-    assertCloseTo(wr.rating, 1482d, 1d)
-    assertCloseTo(br.rating, 1517d, 1d)
-    assertCloseTo(wr.ratingDeviation, 78d, 1d)
-    assertCloseTo(br.ratingDeviation, 78d, 1d)
+    assertCloseTo(wr.rating, 1481d, 1d)
+    assertCloseTo(br.rating, 1519d, 1d)
+    assertCloseTo(wr.ratingDeviation, 78.0967d, 0.0001d)
+    assertCloseTo(br.ratingDeviation, 78.0967d, 0.0001d)
     assertCloseTo(wr.volatility, 0.06, 0.00001d)
     assertCloseTo(br.volatility, 0.06, 0.00001d)
   }
   test("low deviation: draw") {
     val wr = perf.toRating
     val br = perf.toRating
     updateRatings(wr, br, None)
-    assertCloseTo(wr.rating, 1500d, 1d)
-    assertCloseTo(br.rating, 1500d, 1d)
-    assertCloseTo(wr.ratingDeviation, 78d, 1d)
-    assertCloseTo(br.ratingDeviation, 78d, 1d)
+    assertCloseTo(wr.rating, 1498d, 1d)
+    assertCloseTo(br.rating, 1502d, 1d)
+    assertCloseTo(wr.ratingDeviation, 78.0967d, 0.0001d)
+    assertCloseTo(br.ratingDeviation, 78.0967d, 0.0001d)
     assertCloseTo(wr.volatility, 0.06, 0.00001d)
     assertCloseTo(br.volatility, 0.06, 0.00001d)
   }
@@ -116,9 +115,9 @@ class RatingCalculatorTest extends lila.common.LilaTest:
       val br = bP.toRating
       updateRatings(wr, br, White.some)
       assertCloseTo(wr.rating, 1422d, 1d)
-      assertCloseTo(br.rating, 1506d, 1d)
-      assertCloseTo(wr.ratingDeviation, 77d, 1d)
-      assertCloseTo(br.ratingDeviation, 105d, 1d)
+      assertCloseTo(br.rating, 1509d, 1d)
+      assertCloseTo(wr.ratingDeviation, 77.3966, 0.0001d)
+      assertCloseTo(br.ratingDeviation, 105.5926, 0.0001d)
       assertCloseTo(wr.volatility, 0.06, 0.00001d)
       assertCloseTo(br.volatility, 0.065, 0.00001d)
     }
@@ -127,20 +126,20 @@ class RatingCalculatorTest extends lila.common.LilaTest:
       val br = bP.toRating
       updateRatings(wr, br, Black.some)
       assertCloseTo(wr.rating, 1389d, 1d)
-      assertCloseTo(br.rating, 1568d, 1d)
-      assertCloseTo(wr.ratingDeviation, 78d, 1d)
-      assertCloseTo(br.ratingDeviation, 105d, 1d)
+      assertCloseTo(br.rating, 1571d, 1d)
+      assertCloseTo(wr.ratingDeviation, 77.3966, 0.0001d)
+      assertCloseTo(br.ratingDeviation, 105.5926, 0.0001d)
       assertCloseTo(wr.volatility, 0.06, 0.00001d)
       assertCloseTo(br.volatility, 0.065, 0.00001d)
     }
     test("mixed ratings and deviations: draw") {
       val wr = wP.toRating
       val br = bP.toRating
       updateRatings(wr, br, None)
-      assertCloseTo(wr.rating, 1406d, 1d)
-      assertCloseTo(br.rating, 1537d, 1d)
-      assertCloseTo(wr.ratingDeviation, 78d, 1d)
-      assertCloseTo(br.ratingDeviation, 105.87d, 0.01d)
+      assertCloseTo(wr.rating, 1405d, 1d)
+      assertCloseTo(br.rating, 1540d, 1d)
+      assertCloseTo(wr.ratingDeviation, 77.3966, 0.0001d)
+      assertCloseTo(br.ratingDeviation, 105.5926, 0.0001d)
       assertCloseTo(wr.volatility, 0.06, 0.00001d)
       assertCloseTo(br.volatility, 0.065, 0.00001d)
     }
@@ -164,32 +163,32 @@ class RatingCalculatorTest extends lila.common.LilaTest:
       val wr = wP.toRating
       val br = bP.toRating
       updateRatings(wr, br, White.some)
-      assertCloseTo(wr.rating, 1216.7d, 0.1d)
-      assertCloseTo(br.rating, 1636d, 0.1d)
-      assertCloseTo(wr.ratingDeviation, 59.9d, 0.1d)
-      assertCloseTo(br.ratingDeviation, 196.9d, 0.1d)
+      assertCloseTo(wr.rating, 1216.6d, 0.1d)
+      assertCloseTo(br.rating, 1638.4d, 0.1d)
+      assertCloseTo(wr.ratingDeviation, 59.8839d, 0.0001d)
+      assertCloseTo(br.ratingDeviation, 196.3840, 0.0001d)
       assertCloseTo(wr.volatility, 0.053013, 0.000001d)
       assertCloseTo(br.volatility, 0.062028, 0.000001d)
     }
     test("more mixed ratings and deviations: black wins") {
       val wr = wP.toRating
       val br = bP.toRating
       updateRatings(wr, br, Black.some)
-      assertCloseTo(wr.rating, 1199.3d, 0.1d)
-      assertCloseTo(br.rating, 1855.4d, 0.1d)
-      assertCloseTo(wr.ratingDeviation, 59.9d, 0.1d)
-      assertCloseTo(br.ratingDeviation, 196.9d, 0.1d)
+      assertCloseTo(wr.rating, 1199.2d, 0.1d)
+      assertCloseTo(br.rating, 1856.5d, 0.1d)
+      assertCloseTo(wr.ratingDeviation, 59.8839d, 0.0001d)
+      assertCloseTo(br.ratingDeviation, 196.3840, 0.0001d)
       assertCloseTo(wr.volatility, 0.052999, 0.000001d)
       assertCloseTo(br.volatility, 0.061999, 0.000001d)
     }
     test("more mixed ratings and deviations: draw") {
       val wr = wP.toRating
       val br = bP.toRating
       updateRatings(wr, br, None)
-      assertCloseTo(wr.rating, 1208.0, 0.1d)
-      assertCloseTo(br.rating, 1745.7, 0.1d)
-      assertCloseTo(wr.ratingDeviation, 59.90056, 0.1d)
-      assertCloseTo(br.ratingDeviation, 196.98729, 0.1d)
+      assertCloseTo(wr.rating, 1207.9, 0.1d)
+      assertCloseTo(br.rating, 1747.5, 0.1d)
+      assertCloseTo(wr.ratingDeviation, 59.8839, 0.0001d)
+      assertCloseTo(br.ratingDeviation, 196.3840, 0.0001d)
       assertCloseTo(wr.volatility, 0.053002, 0.000001d)
       assertCloseTo(br.volatility, 0.062006, 0.000001d)
     }