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Linear formula for w. Bench: 3328507 (#2239)

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In Stockfish, both the middlegame and endgame bonus for a passed pawn are calculated as a product of two factors. The first is k, chosen based on the presence of defended and unsafe squares. The second is w, a quadratic function of the pawn's rank. Both are only applied if the pawn's relative rank is at least RANK_4.

It does not appear that the complexity of a quadratic function is necessary for w. Here, we replace it with a simpler linear one, which performs equally at both STC and LTC.

STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 46814 W: 10386 L: 10314 D: 26114
http://tests.stockfishchess.org/tests/view/5d29686e0ebc5925cf0d76a1

LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 82372 W: 13845 L: 13823 D: 54704
http://tests.stockfishchess.org/tests/view/5d2980650ebc5925cf0d7bfd

Bench: 3328507
This commit is contained in:
31m059 2019-07-14 08:40:45 -04:00 • committed by Marco Costalba
parent ff69d570d7
commit a0360cc2d4
1 changed files with 1 additions and 1 deletions
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2
src/evaluate.cpp
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@ -622,7 +622,7 @@ namespace {
if (r > RANK_3) if (r > RANK_3)
{ {
int w = (r-2) * (r-2) + 2; int w = 5 * r - 13;
Square blockSq = s + Up; Square blockSq = s + Up;
// Adjust bonus based on the king's proximity // Adjust bonus based on the king's proximity