Fine tune late move reduction logic

kelseyde · May 11, 2024 · affd96e · affd96e
1 parent 188e653
commit affd96e
Show file tree

Hide file tree

Showing 6 changed files with 37 additions and 4 deletions.
diff --git a/src/main/java/com/kelseyde/calvin/engine/EngineConfig.java b/src/main/java/com/kelseyde/calvin/engine/EngineConfig.java
@@ -28,17 +28,22 @@ public class EngineConfig {
     boolean searchCancelled = false;
 
     int maxDepth;
+    int maxPossibleMoves = 250;
     int aspMargin;
     int aspFailMargin;
     int nmpDepth;
     int fpDepth;
     int rfpDepth;
     int lmrDepth;
+    float lmrBase;
+    float lmrDivisor;
+    int lmrMinSearchedMoves;
     int lmpDepth;
     int lmpMultiplier;
     int iirDepth;
     int nmpMargin;
     int dpMargin;
+    int[][] lmrReductions;
     int[] fpMargin;
     int[] rfpMargin;
 
@@ -72,4 +77,19 @@ public class EngineConfig {
 
     int tempoBonus;
 
+    public void postInitialise() {
+        calculateLmrReductions();
+    }
+
+    private void calculateLmrReductions() {
+        // Credit to Lynx (https://github.com/lynx-chess/Lynx) for this formula for determining the optimal late move reduction depth
+        lmrReductions = new int[maxDepth][];
+        for (int depth = 1; depth < maxDepth; ++depth) {
+            lmrReductions[depth] = new int[maxPossibleMoves];
+            for (int movesSearched = 1; movesSearched < maxPossibleMoves; ++movesSearched) {
+                lmrReductions[depth][movesSearched] = (int) Math.round(lmrBase + (Math.log(movesSearched) * Math.log(depth) / lmrDivisor));
+            }
+        }
+    }
+
 }
diff --git a/src/main/java/com/kelseyde/calvin/engine/EngineInitializer.java b/src/main/java/com/kelseyde/calvin/engine/EngineInitializer.java
@@ -31,6 +31,7 @@ public class EngineInitializer {
 
     public static Engine loadEngine() {
         EngineConfig config = loadDefaultConfig();
+        config.postInitialise();
         OpeningBook book = loadDefaultOpeningBook();
         Supplier<MoveGeneration> moveGenerator = MoveGenerator::new;
         Supplier<MoveOrdering> moveOrderer = MoveOrderer::new;

diff --git a/src/main/java/com/kelseyde/calvin/search/Searcher.java b/src/main/java/com/kelseyde/calvin/search/Searcher.java
@@ -21,6 +21,7 @@
 
 import java.time.Duration;
 import java.time.Instant;
+import java.util.Arrays;
 import java.util.List;
 
 /**
@@ -276,8 +277,8 @@ public int search(int depth, int ply, int alpha, int beta, boolean allowNull) {
                 // capture or promotion, let's assume it's less likely to be good, and fully skip searching that move.
                 if (!pvNode
                     && !isInCheck
-                    && depth <= config.getLmpDepth()
                     && isQuiet
+                    && depth <= config.getLmpDepth()
                     && i >= depth * config.getLmpMultiplier()) {
                     board.unmakeMove();
                     continue;
@@ -286,9 +287,14 @@ public int search(int depth, int ply, int alpha, int beta, boolean allowNull) {
                 // capture or promotion, let's save time by assuming it's less likely to be good, and reduce the search depth.
                 int reduction = 0;
                 if (depth >= config.getLmrDepth()
-                    && i >= 2
+                    && i >= (pvNode ? config.getLmrMinSearchedMoves() : config.getLmrMinSearchedMoves() - 1)
                     && isQuiet) {
-                    reduction = i < 5 ? 1 : depth / 3;
+                    reduction = config.getLmrReductions()[depth][i];
+                    if (pvNode || isInCheck) {
+                        reduction--;
+                    }
+                    //System.out.printf("depth %s, moves searched %s, reduction %s%n", depth, i, reduction);
+                    //reduction = i < 5 ? 1 : depth / 3;
                 }
 
                 // For all other moves apart from the principal variation, search with a null window (-alpha - 1, -alpha),

diff --git a/src/main/resources/engine_config.json b/src/main/resources/engine_config.json
@@ -17,6 +17,9 @@
   "fpDepth":6,
   "rfpDepth":4,
   "lmrDepth":3,
+  "lmrMinSearchedMoves": 3,
+  "lmrBase": 0.85,
+  "lmrDivisor": 3.12,
   "lmpDepth":2,
   "lmpMultiplier":10,
   "iirDepth":4,

diff --git a/src/test/java/com/kelseyde/calvin/utils/TestUtils.java b/src/test/java/com/kelseyde/calvin/utils/TestUtils.java
@@ -57,7 +57,9 @@ private static EngineConfig loadConfig(String configLocation) {
             ObjectMapper mapper = new ObjectMapper();
             Path path = Paths.get(configLocation);
             String json = Files.readString(path);
-            return mapper.readValue(json, EngineConfig.class);
+            EngineConfig config = mapper.readValue(json, EngineConfig.class);
+            config.postInitialise();
+            return config;
         } catch (IOException e) {
             throw new RuntimeException(e);
         }

diff --git a/src/test/resources/sperft/starting_position/sperft_depth_15.csv b/src/test/resources/sperft/starting_position/sperft_depth_15.csv
@@ -142,3 +142,4 @@ timestamp,performance
 2024-05-09T12:55:01Z,PT8.864766S
 2024-05-09T12:55:14Z,PT8.680054S
 2024-05-09T13:01:47Z,PT6.410241S
+2024-05-11T17:49:51Z,PT4.587096S