This patch adds the tropism measure as a new term in the king danger variable.
Since we then trasform this variable as a Score via a quadratic formula, the
main effect of the patch is the positive correlation of the tropism measure
with some checks and pins information already present in the king danger code.
STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 6805 W: 1597 L: 1431 D: 3777
http://tests.stockfishchess.org/tests/view/
5b5df8d10ebc5902bdb91699
LTC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 32872 W: 5782 L: 5523 D: 21567
http://tests.stockfishchess.org/tests/view/
5b5e08d80ebc5902bdb917ee
How to continue from there?
• it may be possible to use CloseEnemies=S(7,0)
• we may want to try incorporating other strategic features in the quadratic
king danger.
Closes https://github.com/official-stockfish/Stockfish/pull/1717
Bench:
5591925
: AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
const Square ksq = pos.square<KING>(Us);
: AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
const Square ksq = pos.square<KING>(Us);
- Bitboard weak, b, b1, b2, safe, unsafeChecks;
+ Bitboard kingFlank, weak, b, b1, b2, safe, unsafeChecks;
// King shelter and enemy pawns storm
Score score = pe->king_safety<Us>(pos, ksq);
// King shelter and enemy pawns storm
Score score = pe->king_safety<Us>(pos, ksq);
+ // Find the squares that opponent attacks in our king flank, and the squares
+ // which are attacked twice in that flank but not defended by our pawns.
+ kingFlank = KingFlank[file_of(ksq)];
+ b1 = attackedBy[Them][ALL_PIECES] & kingFlank & Camp;
+ b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
+
+ int tropism = popcount(b1) + popcount(b2);
+
// Main king safety evaluation
if (kingAttackersCount[Them] > 1 - pos.count<QUEEN>(Them))
{
// Main king safety evaluation
if (kingAttackersCount[Them] > 1 - pos.count<QUEEN>(Them))
{
+ 69 * kingAttacksCount[Them]
+ 185 * popcount(kingRing[Us] & weak)
+ 129 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
+ 69 * kingAttacksCount[Them]
+ 185 * popcount(kingRing[Us] & weak)
+ 129 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
- 873 * !pos.count<QUEEN>(Them)
- 6 * mg_value(score) / 8
- 873 * !pos.count<QUEEN>(Them)
- 6 * mg_value(score) / 8
// Transform the kingDanger units into a Score, and subtract it from the evaluation
if (kingDanger > 0)
// Transform the kingDanger units into a Score, and subtract it from the evaluation
if (kingDanger > 0)
- Bitboard kf = KingFlank[file_of(ksq)];
-
// Penalty when our king is on a pawnless flank
// Penalty when our king is on a pawnless flank
- if (!(pos.pieces(PAWN) & kf))
+ if (!(pos.pieces(PAWN) & kingFlank))
- // Find the squares that opponent attacks in our king flank, and the squares
- // which are attacked twice in that flank but not defended by our pawns.
- b1 = attackedBy[Them][ALL_PIECES] & kf & Camp;
- b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
-
- // King tropism, to anticipate slow motion attacks on our king
- score -= CloseEnemies * (popcount(b1) + popcount(b2));
+ // King tropism bonus, to anticipate slow motion attacks on our king
+ score -= CloseEnemies * tropism;
if (T)
Trace::add(KING, Us, score);
if (T)
Trace::add(KING, Us, score);