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Introduce tropism measure in king danger

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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
This commit is contained in:
Stéphane Nicolet 2018-07-30 01:41:04 +02:00
parent c08e05b494
commit ba2a2c34bb
1 changed files with 14 additions and 12 deletions
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26
src/evaluate.cpp
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@ -413,11 +413,19 @@ namespace {
: 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);
// 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))
{
@ -470,9 +478,10 @@ namespace {
+ 69 * kingAttacksCount[Them]
+ 185 * popcount(kingRing[Us] & weak)
+ 129 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
+ 4 * tropism
- 873 * !pos.count<QUEEN>(Them)
- 6 * mg_value(score) / 8
- 2 ;
- 30;
// Transform the kingDanger units into a Score, and subtract it from the evaluation
if (kingDanger > 0)
@ -483,19 +492,12 @@ namespace {
}
}
Bitboard kf = KingFlank[file_of(ksq)];
// Penalty when our king is on a pawnless flank
if (!(pos.pieces(PAWN) & kf))
if (!(pos.pieces(PAWN) & kingFlank))
score -= PawnlessFlank;
// 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);