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Scale down eval for queen imbalance

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We lower the endgame value of the evaluation when we detect that there
is only one queen left on the board (more precisely, we use a scale
factor of 37/64, or about 0.58, for the endgame part of the evaluation).
Hopefully this helps a little bit for the assessment of positions with
queen imbalance, which are one of the well-known Stockfish weaknesses.

STC:
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 21600 W: 4176 L: 3955 D: 13469
Ptnml(0-2): 351, 2457, 5003, 2598, 391
https://tests.stockfishchess.org/tests/view/5ef871b6020eec13834a94e8

LTC:
LLR: 2.97 (-2.94,2.94) {0.25,1.75}
Total: 248328 W: 30596 L: 29720 D: 188012
Ptnml(0-2): 1544, 22345, 75665, 22911, 1699
https://tests.stockfishchess.org/tests/view/5ef87aec020eec13834a94fe

Closes https://github.com/official-stockfish/Stockfish/pull/2781

Bench: 4441323
This commit is contained in:
Stéphane Nicolet 2020-06-28 22:24:57 +02:00
parent 16836f39b2
commit c7194bd924
1 changed files with 3 additions and 2 deletions
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5
src/evaluate.cpp
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@ -767,7 +767,6 @@ namespace {
eg += v;
// Compute the scale factor for the winning side
Color strongSide = eg > VALUE_DRAW ? WHITE : BLACK;
int sf = me->scale_factor(pos, strongSide);
@ -782,13 +781,15 @@ namespace {
else
sf = 22 + 3 * pos.count<ALL_PIECES>(strongSide);
}
else if( pos.non_pawn_material(WHITE) == RookValueMg
else if ( pos.non_pawn_material(WHITE) == RookValueMg
&& pos.non_pawn_material(BLACK) == RookValueMg
&& !pe->passed_pawns(strongSide)
&& pos.count<PAWN>(strongSide) - pos.count<PAWN>(~strongSide) <= 1
&& bool(KingSide & pos.pieces(strongSide, PAWN)) != bool(QueenSide & pos.pieces(strongSide, PAWN))
&& (attacks_bb<KING>(pos.square<KING>(~strongSide)) & pos.pieces(~strongSide, PAWN)))
sf = 36;
else if (pos.count<QUEEN>() == 1)
sf = 37;
else
sf = std::min(sf, 36 + 7 * pos.count<PAWN>(strongSide));
}