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Switch to NNUE eval probabilistically for OCB

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Introduce a small chance of switching to NNUE if PSQ imbalance is large but we have opposite colored bishops and the classical eval is struggling to win.

STC:
LLR: 2.94 (-2.94,2.94) {-0.25,1.25}
Total: 25304 W: 3179 L: 2983 D: 19142
Ptnml(0-2): 172, 2171, 7781, 2345, 183
https://tests.stockfishchess.org/tests/view/5f6b14dec7759d4ee307cfe3

LTC:
LLR: 2.94 (-2.94,2.94) {0.25,1.25}
Total: 84680 W: 4846 L: 4556 D: 75278
Ptnml(0-2): 89, 3933, 34011, 4213, 94
https://tests.stockfishchess.org/tests/view/5f6b3fb6c7759d4ee307cff9

closes https://github.com/official-stockfish/Stockfish/pull/3146

Bench: 3865413
This commit is contained in:
SFisGOD
2020-09-23 14:00:42 +08:00
committed by Joost VandeVondele
parent 5e6a5e48e6
commit f66c381f11
1 changed files with 9 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

13
src/evaluate.cpp
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@@ -1021,10 +1021,10 @@ Value Eval::evaluate(const Position& pos) {
v = Evaluation<NO_TRACE>(pos).value();
else
{
// scale and shift NNUE for compatibility with search and classical evaluation
// Scale and shift NNUE for compatibility with search and classical evaluation
auto adjusted_NNUE = [&](){ return NNUE::evaluate(pos) * 5 / 4 + Tempo; };
// if there is PSQ imbalance use classical eval, with small probability if it is small
// If there is PSQ imbalance use classical eval, with small probability if it is small
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;
@@ -1032,9 +1032,14 @@ Value Eval::evaluate(const Position& pos) {
v = classical ? Evaluation<NO_TRACE>(pos).value() : adjusted_NNUE();
// if the classical eval is small and imbalance large, use NNUE nevertheless.
// 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
&& abs(v) * 16 < NNUEThreshold2 * r50)
&& (abs(v) * 16 < NNUEThreshold2 * r50
|| ( pos.opposite_bishops()
&& abs(v) * 16 < (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50
&& !(pos.this_thread()->nodes & 0xB))))
v = adjusted_NNUE();
}