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Detect fortresses a little bit quicker 

In the so-called "hybrid" method of evaluation of current master, we use the
classical eval (because of its speed) instead of the NNUE eval when the classical
material balance approximation hints that the position is "winning enough" to
rely on the classical eval.

This trade-off idea between speed and accuracy works well in general, but in
some fortress positions the classical eval is just bad. So in shuffling branches
of the search tree, we (slowly) increase the thresehold so that eventually we
don't trust classical anymore and switch to NNUE evaluation.

This patch increases that threshold faster, so that we switch to NNUE quicker
in shuffling branches. Idea is to incite Stockfish to spend less time in fortresses
lines in the search tree, and spend more time searching the critical lines.

passed STC:
LLR: 2.96 (-2.94,2.94) <-0.50,2.50>
Total: 47872 W: 3908 L: 3720 D: 40244
Ptnml(0-2): 122, 3053, 17419, 3199, 143
https://tests.stockfishchess.org/tests/view/60cef34b457376eb8bcab79d

passed LTC:
LLR: 2.93 (-2.94,2.94) <0.50,3.50>
Total: 73616 W: 2326 L: 2143 D: 69147
Ptnml(0-2): 21, 1940, 32705, 2119, 23
https://tests.stockfishchess.org/tests/view/60cf6d842114332881e73528

Retested at LTC against lastest master:
LLR: 2.93 (-2.94,2.94) <0.50,3.50>
Total: 18264 W: 642 L: 532 D: 17090
Ptnml(0-2): 6, 479, 8055, 583, 9
https://tests.stockfishchess.org/tests/view/60d18cd540925195e7a6c351

closes https://github.com/official-stockfish/Stockfish/pull/3578

Bench: 5139233
pull/3584/head
Stéphane Nicolet 2021-06-22 09:08:37 +02:00
parent 9b82414b67
commit 0470bcef0e
1 changed files with 7 additions and 8 deletions
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15
src/evaluate.cpp
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@ -192,8 +192,7 @@ namespace {
// Threshold for lazy and space evaluation
constexpr Value LazyThreshold1 = Value(1565);
constexpr Value LazyThreshold2 = Value(1102);
constexpr Value SpaceThreshold = Value(11551);
constexpr Value NNUEThreshold1 = Value(800);
constexpr Value SpaceThreshold = Value(11551);
// KingAttackWeights[PieceType] contains king attack weights by piece type
constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 81, 52, 44, 10 };
@ -1103,14 +1102,14 @@ Value Eval::evaluate(const Position& pos) {
return nnue;
};
// If there is PSQ imbalance we use the classical eval.
// If there is PSQ imbalance we use the classical eval, but we switch to
// NNUE eval faster when shuffling or if the material on the board is high.
int r50 = pos.rule50_count();
Value psq = Value(abs(eg_value(pos.psq_score())));
int r50 = 16 + pos.rule50_count();
bool largePsq = psq * 16 > (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50;
v = largePsq ? Evaluation<NO_TRACE>(pos).value() // classical
: adjusted_NNUE(); // NNUE
bool classical = psq * 5 > (750 + pos.non_pawn_material() / 64) * (5 + r50);
v = classical ? Evaluation<NO_TRACE>(pos).value() // classical
: adjusted_NNUE(); // NNUE
}
// Damp down the evaluation linearly when shuffling