Change isolated pawn penalty to allow different values per rank

lynx-chess · May 17, 2024 · c02831d · c02831d
1 parent 19b2ee9
commit c02831d
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Showing 3 changed files with 51 additions and 12 deletions.
diff --git a/src/Lynx.Cli/appsettings.json b/src/Lynx.Cli/appsettings.json
@@ -58,10 +58,6 @@
     "FP_Margin": 250,
 
     // Evaluation
-    "IsolatedPawnPenalty": {
-      "MG": -21,
-      "EG": -17
-    },
     "OpenFileRookBonus": {
       "MG": 46,
       "EG": 9
@@ -131,6 +127,40 @@
         "MG": 0,
         "EG": 0
       }
+    },
+    "IsolatedPawnPenalty": {
+      "Rank0": {
+        "MG": 0,
+        "EG": 0
+      },
+      "Rank1": {
+        "MG": -5,
+        "EG": -5
+      },
+      "Rank2": {
+        "MG": -5,
+        "EG": -5
+      },
+      "Rank3": {
+        "MG": -5,
+        "EG": -5
+      },
+      "Rank4": {
+        "MG": -5,
+        "EG": -5
+      },
+      "Rank5": {
+        "MG": -5,
+        "EG": -5
+      },
+      "Rank6": {
+        "MG": -5,
+        "EG": -5
+      },
+      "Rank7": {
+        "MG": 0,
+        "EG": 0
+      }
     }
     // End of evaluation
   },

diff --git a/src/Lynx/Configuration.cs b/src/Lynx/Configuration.cs
@@ -203,8 +203,6 @@ public sealed class EngineSettings
 
     #region Evaluation
 
-    public TaperedEvaluationTerm IsolatedPawnPenalty { get; set; } = new(-21, -17);
-
     public TaperedEvaluationTerm OpenFileRookBonus { get; set; } = new(46, 9);
 
     public TaperedEvaluationTerm SemiOpenFileRookBonus { get; set; } = new(15, 15);
@@ -233,6 +231,16 @@ public sealed class EngineSettings
         new(104, 243),
         new(0, 0));
 
+    public TaperedEvaluationTermByRank IsolatedPawnPenalty { get; set; } = new(
+        new(0, 0),
+        new(-5, -5),
+        new(-5, -5),
+        new(-5, -5),
+        new(-5, -5),
+        new(-5, -5),
+        new(-5, -5),
+        new(0, 0));
+
     #endregion
 }
 

diff --git a/src/Lynx/Model/Position.cs b/src/Lynx/Model/Position.cs
@@ -867,18 +867,19 @@ private int PawnAdditionalEvaluation(int squareIndex, int pieceIndex)
     {
         int packedBonus = 0;
 
+        var rank = Constants.Rank[squareIndex];
+        if (pieceIndex == (int)Piece.p)
+        {
+            rank = 7 - rank;
+        }
+
         if ((PieceBitBoards[pieceIndex] & Masks.IsolatedPawnMasks[squareIndex]) == default) // isIsolatedPawn
         {
-            packedBonus += Configuration.EngineSettings.IsolatedPawnPenalty.PackedEvaluation;
+            packedBonus += Configuration.EngineSettings.IsolatedPawnPenalty[rank].PackedEvaluation;
         }
 
         if ((PieceBitBoards[(int)Piece.p - pieceIndex] & Masks.PassedPawns[pieceIndex][squareIndex]) == default)    // isPassedPawn
         {
-            var rank = Constants.Rank[squareIndex];
-            if (pieceIndex == (int)Piece.p)
-            {
-                rank = 7 - rank;
-            }
             packedBonus += Configuration.EngineSettings.PassedPawnBonus[rank].PackedEvaluation;
         }