From 5f747c6cd80fee99db12dc26853c8cf0d51e5bde Mon Sep 17 00:00:00 2001
From: Dan Balasescu <smoogipoo@smgi.me>
Date: Mon, 15 Dec 2025 14:56:15 +0900
Subject: [PATCH 1/4] Update test data to produce failing tests

Taken from
https://github.com/vivekjoshy/openskill.py/blob/c9d3210ed068570cfa11a3f56586255c93d1a4c8/tests/models/data/plackettluce.json
---
 .../Models/Data/plackettluce.json              | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/OpenSkillSharp.Tests/Models/Data/plackettluce.json b/OpenSkillSharp.Tests/Models/Data/plackettluce.json
index 2b8d58e..41fe81e 100644
--- a/OpenSkillSharp.Tests/Models/Data/plackettluce.json
+++ b/OpenSkillSharp.Tests/Models/Data/plackettluce.json
@@ -86,21 +86,21 @@
     ],
     "team_2": [
       {
-        "mu": 23.083700519022745,
+        "mu": 20.599656070925114,
         "sigma": 8.222674397835641
       },
       {
-        "mu": 21.717476072569045,
+        "mu": 20.47545384852023,
         "sigma": 8.277466291367071
       }
     ],
     "team_3": [
       {
-        "mu": 21.717476072569045,
+        "mu": 20.47545384852023,
         "sigma": 8.277466291367071
       },
       {
-        "mu": 23.083700519022745,
+        "mu": 20.599656070925114,
         "sigma": 8.222674397835641
       }
     ],
@@ -160,7 +160,7 @@
   "ties": {
     "team_1": [
       {
-        "mu": 23.241111866333558,
+        "mu": 21.63766806988004,
         "sigma": 8.310709773172306
       }
     ],
@@ -176,15 +176,15 @@
     ],
     "team_3": [
       {
-        "mu": 21.479966996534408,
+        "mu": 19.87652320008089,
         "sigma": 8.237522411103104
       },
       {
-        "mu": 21.479966996534408,
+        "mu": 19.87652320008089,
         "sigma": 8.237522411103104
       },
       {
-        "mu": 21.479966996534408,
+        "mu": 19.87652320008089,
         "sigma": 8.237522411103104
       }
     ]
@@ -261,4 +261,4 @@
       }
     ]
   }
-}
\ No newline at end of file
+}

From 2c39577d897bb6038267db6e27a6da00ae69a90f Mon Sep 17 00:00:00 2001
From: Dan Balasescu <smoogipoo@smgi.me>
Date: Mon, 15 Dec 2025 14:57:37 +0900
Subject: [PATCH 2/4] Fix PlackettLuce handling of ties

---
 OpenSkillSharp/Models/PlackettLuce.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/OpenSkillSharp/Models/PlackettLuce.cs b/OpenSkillSharp/Models/PlackettLuce.cs
index 88e4703..f8358d0 100644
--- a/OpenSkillSharp/Models/PlackettLuce.cs
+++ b/OpenSkillSharp/Models/PlackettLuce.cs
@@ -40,7 +40,7 @@ protected override IEnumerable<ITeam> Compute(
                     return (
                         sumOmega: acc.sumOmega + (
                             iTeamIndex == qTeamIndex
-                                ? 1 - (iMuOverCeOverSumQ / rankOccurrences[qTeamIndex])
+                                ? (1 - iMuOverCeOverSumQ) / rankOccurrences[qTeamIndex]
                                 : -1 * iMuOverCeOverSumQ / rankOccurrences[qTeamIndex]
                         ),
                         sumDelta: acc.sumDelta +

From ad9cc65d6b6f5b0d92c550734e3c2ef6b258c4f6 Mon Sep 17 00:00:00 2001
From: Dan Balasescu <smoogipoo@smgi.me>
Date: Mon, 15 Dec 2025 15:06:33 +0900
Subject: [PATCH 3/4] Add another failing test

---
 OpenSkillSharp.Tests/Models/PlackettLuceTests.cs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/OpenSkillSharp.Tests/Models/PlackettLuceTests.cs b/OpenSkillSharp.Tests/Models/PlackettLuceTests.cs
index 549b03c..b199fa8 100644
--- a/OpenSkillSharp.Tests/Models/PlackettLuceTests.cs
+++ b/OpenSkillSharp.Tests/Models/PlackettLuceTests.cs
@@ -149,4 +149,16 @@ public void Rate_Balance()
         // Assert
         Assertions.RatingResultsEqual(expectedRatings, results);
     }
+
+    [Fact]
+    public void Rate_AllScoresTied()
+    {
+        PlackettLuce model = new PlackettLuce { Mu = 30, Sigma = 30.0 / 3 };
+
+        ITeam[] teams = [new Team { Players = [model.Rating()] }, new Team { Players = [model.Rating()] }];
+        ITeam[] result = model.Rate(teams, scores: [0, 0]).ToArray();
+
+        Assert.Equal(30, result[0].Players.Single().Mu);
+        Assert.Equal(30, result[1].Players.Single().Mu);
+    }
 }
\ No newline at end of file

From d551f2fb077cb794eb5ef06601d71b5c5b84a099 Mon Sep 17 00:00:00 2001
From: Dan Balasescu <smoogipoo@smgi.me>
Date: Mon, 15 Dec 2025 15:06:56 +0900
Subject: [PATCH 4/4] Fix exception when all scores are tied

---
 OpenSkillSharp/OpenSkillModelBase.cs | 1 +
 1 file changed, 1 insertion(+)

diff --git a/OpenSkillSharp/OpenSkillModelBase.cs b/OpenSkillSharp/OpenSkillModelBase.cs
index 05c8c85..3ef8f0b 100644
--- a/OpenSkillSharp/OpenSkillModelBase.cs
+++ b/OpenSkillSharp/OpenSkillModelBase.cs
@@ -289,6 +289,7 @@ protected IEnumerable<double> CalculateMarginAdjustedMu(
                     double sign = qTeamScore > iTeamScore ? 1D : -1D;
                     return (qTeam.Mu - iTeam.Mu) * (marginFactor - 1) * sign;
                 })
+                .DefaultIfEmpty(0)
                 .Average();
 
             return qTeam.Mu + muAdjustment;