Sometimes change the (materialist, positional) balance

snicolet · snicolet · commit cefd5b300cc8 · 2021-05-22T20:00:03.000+02:00
Our new nets output two values for the side to move in the last layer. We can interpret the first value as a material evaluation of the position, and the second one as the dynamic, positional value of the location of pieces. This patch changes the balance for the (materialist, positional) parts of the score from (128, 128) to (121, 135) when the piece material is equal between the two players, and keeps the standard (128, 128) balance when one player has at least a quality advantage. Passed STC: LLR: 2.93 (-2.94,2.94) <-0.50,2.50> Total: 15936 W: 1421 L: 1266 D: 13249 Ptnml(0-2): 37, 1037, 5694, 1134, 66 https://tests.stockfishchess.org/tests/view/60a82df9ce8ea25a3ef0408f Passed LTC: LLR: 2.94 (-2.94,2.94) <0.50,3.50> Total: 13904 W: 516 L: 410 D: 12978 Ptnml(0-2): 4, 374, 6088, 484, 2 https://tests.stockfishchess.org/tests/view/60a8bbf9ce8ea25a3ef04101 closes official-stockfish/Stockfish#3492 Bench: 3856635
diff --git a/src/nnue/evaluate_nnue.cpp b/src/nnue/evaluate_nnue.cpp
@@ -158,13 +158,26 @@ namespace Stockfish::Eval::NNUE {
     ASSERT_ALIGNED(buffer, alignment);
 
     const std::size_t bucket = (pos.count<ALL_PIECES>() - 1) / 4;
-
     const auto [psqt, lazy] = featureTransformer->transform(pos, transformedFeatures, bucket);
-    if (lazy) {
+    
+    if (lazy)
       return static_cast<Value>(psqt / OutputScale);
-    } else {
+    else 
+    {
       const auto output = network[bucket]->propagate(transformedFeatures, buffer);
-      return static_cast<Value>((output[0] + psqt) / OutputScale);
+
+      int materialist = psqt;
+      int positional  = output[0];
+
+      int delta_npm = abs(pos.non_pawn_material(WHITE) - pos.non_pawn_material(BLACK));
+      int entertainment = (delta_npm <= BishopValueMg - KnightValueMg ? 7 : 0);
+
+      int A = 128 - entertainment;
+      int B = 128 + entertainment;
+
+      int sum = (A * materialist + B * positional) / 128;
+
+      return static_cast<Value>( sum / OutputScale );
     }
   }
 
