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Tweak nnue scaling to keep more material

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Current master uses a constant scale factor of 5/4 = 1.25 for the output
of the NNUE network, for compatibility with search and classical evaluation.
We modify this scale factor to make it dependent on the phase of the game,
going from about 1.5 in the opening to 1.0 for pure pawn endgames.

This helps Stockfish to avoid exchanges of pieces (heavy pieces in particular)
when she has the advantage, keeping more material on the board when attacking.

Passed STC:
LLR: 2.95 (-2.94,2.94) {-0.25,1.25}
Total: 14744 W: 1771 L: 1599 D: 11374
Ptnml(0-2): 87, 1184, 4664, 1344, 93
https://tests.stockfishchess.org/tests/view/5f6fb0a63b22d6afa506904f

Passed LTC:
LLR: 2.95 (-2.94,2.94) {0.25,1.25}
Total: 8912 W: 512 L: 393 D: 8007
Ptnml(0-2): 7, 344, 3637, 459, 9
https://tests.stockfishchess.org/tests/view/5f6fcf533b22d6afa5069066

closes https://github.com/official-stockfish/Stockfish/pull/3154

Bench: 3943952
This commit is contained in:
Stéphane Nicolet 2020-09-26 23:19:53 +02:00 • committed by Joost VandeVondele
parent f66c381f11
commit 1dbd2a1ad5
1 changed files with 5 additions and 2 deletions
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7
src/evaluate.cpp
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@ -1022,7 +1022,10 @@ Value Eval::evaluate(const Position& pos) {
else
{
// Scale and shift NNUE for compatibility with search and classical evaluation
auto adjusted_NNUE = [&](){ return NNUE::evaluate(pos) * 5 / 4 + Tempo; };
auto adjusted_NNUE = [&](){
int mat = pos.non_pawn_material();
return NNUE::evaluate(pos) * (1024 + mat / 32) / 1024 + Tempo;
};
// If there is PSQ imbalance use classical eval, with small probability if it is small
Value psq = Value(abs(eg_value(pos.psq_score())));
@ -1037,7 +1040,7 @@ Value Eval::evaluate(const Position& pos) {
// small probability if the classical eval is less than the threshold.
if ( largePsq
&& (abs(v) * 16 < NNUEThreshold2 * r50
|| ( pos.opposite_bishops()
|| ( pos.opposite_bishops()
&& abs(v) * 16 < (NNUEThreshold1 + pos.non_pawn_material() / 64) * r50
&& !(pos.this_thread()->nodes & 0xB))))
v = adjusted_NNUE();