Tweak optimism with complexity

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index c1d3d159b6fa0de652da30c638c2823bf2f99cdf..edff9185c2da180e33c8931e5673ce561fc1bb81 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -1082,23 +1082,28 @@ make_v:
 Value Eval::evaluate(const Position& pos) {
 
   Value v;
+  bool useClassical = false;
 
-  // Deciding between classical and NNUE eval: for high PSQ imbalance we use classical,
+  // Deciding between classical and NNUE eval (~10 Elo): for high PSQ imbalance we use classical,
   // but we switch to NNUE during long shuffling or with high material on the board.
-
   if (  !useNNUE
       || abs(eg_value(pos.psq_score())) * 5 > (850 + pos.non_pawn_material() / 64) * (5 + pos.rule50_count()))
-      v = Evaluation<NO_TRACE>(pos).value();          // classical
-  else
   {
-       int scale =   898
-                   + 24 * pos.count<PAWN>()
-                   + 33 * pos.non_pawn_material() / 1024;
+      v = Evaluation<NO_TRACE>(pos).value();          // classical
+      useClassical = abs(v) >= 300;
+  }
 
+  // If result of a classical evaluation is much lower than threshold fall back to NNUE
+  if (useNNUE && !useClassical)
+  {
        Value nnue     = NNUE::evaluate(pos, true);     // NNUE
+       int scale      = 1136 + 20 * pos.non_pawn_material() / 1024;
        Color stm      = pos.side_to_move();
        Value optimism = pos.this_thread()->optimism[stm];
+       Value psq      = (stm == WHITE ? 1 : -1) * eg_value(pos.psq_score());
+       int complexity = abs(nnue - psq) / 256;
 
+       optimism *= (1 + complexity);
        v = (nnue + optimism) * scale / 1024 - optimism;
 
        if (pos.is_chess960())