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Simplify NNUE / classical evaluation selection 

for the new network architecture these rules can be simplified,
closer to the original PSQT difference based again.

passed STC
LLR: 2.94 (-2.94,2.94) <-2.50,0.50>
Total: 22656 W: 1979 L: 1868 D: 18809
Ptnml(0-2): 70, 1496, 8087, 1603, 72
https://tests.stockfishchess.org/tests/view/60b24579db3c4776cb89d122

passed LTC
LLR: 2.93 (-2.94,2.94) <-2.50,0.50>
Total: 30224 W: 1015 L: 953 D: 28256
Ptnml(0-2): 4, 860, 13330, 906, 12
https://tests.stockfishchess.org/tests/view/60b27613db3c4776cb89d145

closes https://github.com/official-stockfish/Stockfish/pull/3511

Bench: 3937626
pull/3512/head
Joost VandeVondele 2021-05-29 15:44:57 +02:00
parent 6174a37a37
commit 4c02998325
1 changed files with 3 additions and 19 deletions
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22
src/evaluate.cpp
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@ -218,7 +218,6 @@ namespace {
constexpr Value LazyThreshold2 = Value(1102);
constexpr Value SpaceThreshold = Value(11551);
constexpr Value NNUEThreshold1 = Value(800);
constexpr Value NNUEThreshold2 = Value(176);
// KingAttackWeights[PieceType] contains king attack weights by piece type
constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 81, 52, 44, 10 };
@ -1127,29 +1126,14 @@ Value Eval::evaluate(const Position& pos) {
return nnue;
};
// If there is PSQ imbalance we use the classical eval. We also introduce
// a small probability of using the classical eval when PSQ imbalance is small.
// If there is PSQ imbalance we use the classical eval.
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;
// Use classical evaluation for really low piece endgames.
// One critical case is the draw for bishop + A/H file pawn vs naked king.
bool lowPieceEndgame = pos.non_pawn_material() == BishopValueMg
|| (pos.non_pawn_material() < 2 * RookValueMg && pos.count<PAWN>() < 2);
v = largePsq ? Evaluation<NO_TRACE>(pos).value() // classical
: adjusted_NNUE(); // NNUE
v = largePsq || lowPieceEndgame ? Evaluation<NO_TRACE>(pos).value() // classical
: adjusted_NNUE(); // NNUE
// If the classical eval is small and imbalance large, use NNUE nevertheless.
// For the case of opposite colored bishops, switch to NNUE eval with small
// probability if the classical eval is less than the threshold.
if ( largePsq
&& !lowPieceEndgame
&& ( abs(v) * 16 < NNUEThreshold2 * r50
|| ( pos.opposite_bishops()
&& abs(v) * 16 < (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50)))
v = adjusted_NNUE();
}
// Damp down the evaluation linearly when shuffling