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Add a specific FRC correction from classical to NNUE

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our net currently is not trained on FRC games, and so doesn't know about the important pattern of a bishop that is cornered in FRC.
This patch introduces a term we have in the classical evaluation for this case, and adds it to the NNUE eval.

Since fishtest doesn't support FRC right now, the patch was tested locally at STC conditions,
starting from the book of FRC starting positions.

Score of master vs patch: 993 - 2226 - 6781  [0.438] 10000

Which corresponds to approximately 40 Elo

The patch passes non-regression testing for traditional chess (where it adds one branch).

passed STC:
https://tests.stockfishchess.org/tests/view/604fa2532433018de7a38b67
LLR: 2.95 (-2.94,2.94) {-1.25,0.25}
Total: 30560 W: 2701 L: 2636 D: 25223
Ptnml(0-2): 88, 2056, 10921, 2133, 82

passed STC also in an earlier version:
https://tests.stockfishchess.org/tests/view/604f61282433018de7a38b4d

closes https://github.com/official-stockfish/Stockfish/pull/3398

No functional change
This commit is contained in:
Vizvezdenec 2021-03-15 19:05:01 +01:00 • committed by Joost VandeVondele
parent 5089061659
commit ace9632c67
1 changed files with 45 additions and 1 deletions
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46
src/evaluate.cpp
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@ -1038,6 +1038,45 @@ make_v:
return v;
}
// specifically correct for cornered bishops to fix FRC with NNUE.
Value fix_FRC(const Position& pos) {
Value bAdjust = Value(0);
constexpr Value p1=Value(209), p2=Value(136), p3=Value(148);
Color Us = pos.side_to_move();
if ( (pos.pieces(Us, BISHOP) & relative_square(Us, SQ_A1))
&& (pos.pieces(Us, PAWN) & relative_square(Us, SQ_B2)))
{
bAdjust -= !pos.empty(relative_square(Us,SQ_B3)) ? p1
: pos.piece_on(relative_square(Us,SQ_C3)) == make_piece(Us, PAWN) ? p2
: p3;
}
if ( (pos.pieces(Us, BISHOP) & relative_square(Us, SQ_H1))
&& (pos.pieces(Us, PAWN) & relative_square(Us, SQ_G2)))
{
bAdjust -= !pos.empty(relative_square(Us,SQ_G3)) ? p1
: pos.piece_on(relative_square(Us,SQ_F3)) == make_piece(Us, PAWN) ? p2
: p3;
}
if ( (pos.pieces(~Us, BISHOP) & relative_square(Us, SQ_A8))
&& (pos.pieces(~Us, PAWN) & relative_square(Us, SQ_B7)))
{
bAdjust += !pos.empty(relative_square(Us,SQ_B6)) ? p1
: pos.piece_on(relative_square(Us,SQ_C6)) == make_piece(~Us, PAWN) ? p2
: p3;
}
if ( (pos.pieces(~Us, BISHOP) & relative_square(Us, SQ_H8))
&& (pos.pieces(~Us, PAWN) & relative_square(Us, SQ_G7)))
{
bAdjust += !pos.empty(relative_square(Us,SQ_G6)) ? p1
: pos.piece_on(relative_square(Us,SQ_F6)) == make_piece(~Us, PAWN) ? p2
: p3;
}
return bAdjust;
}
} // namespace
@ -1055,7 +1094,12 @@ Value Eval::evaluate(const Position& pos) {
// Scale and shift NNUE for compatibility with search and classical evaluation
auto adjusted_NNUE = [&](){
int mat = pos.non_pawn_material() + 2 * PawnValueMg * pos.count<PAWN>();
return NNUE::evaluate(pos) * (641 + mat / 32 - 4 * pos.rule50_count()) / 1024 + Tempo;
Value nnueValue = NNUE::evaluate(pos) * (641 + mat / 32 - 4 * pos.rule50_count()) / 1024 + Tempo;
if (pos.is_chess960())
nnueValue += fix_FRC(pos);
return nnueValue;
};
// If there is PSQ imbalance use classical eval, with small probability if it is small