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Scale down endgame factor when shuffling

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This patch decreases the endgame scale factor using the 50 moves counter.
Looking at some games with this patch, it seems to have two effects on
the playing style:

1) when no progress can be made in late endgames (for instance in fortresses
   or opposite bishops endgames) the evaluation will be largely tamed down
   towards a draw value.

2) more interestingly, there is also a small effect in the midgame play because
   Stockfish will panic a little bit if there are more than four consecutive
   shuffling moves with an advantage: the engine will try to move a pawn or to
   exchange a piece to keep the advantage, so the follow-ups of the position
   will be discovered earlier by the alpha-beta search.

passed STC:
LLR: 2.95 (-2.94,2.94) [0.50,4.50]
Total: 23017 W: 5080 L: 4805 D: 13132
http://tests.stockfishchess.org/tests/view/5d7e4aef0ebc59069c36fc74

passed LTC:
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 30746 W: 5171 L: 4911 D: 20664
http://tests.stockfishchess.org/tests/view/5d7e513d0ebc59069c36ff26

Pull request: https://github.com/official-stockfish/Stockfish/pull/2304

Bench: 4272173
This commit is contained in:
Stéphane Nicolet 2019-09-15 23:18:54 +02:00
parent 843a6c4305
commit 7b06475294
1 changed files with 2 additions and 1 deletions
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3
src/evaluate.cpp
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@ -769,8 +769,9 @@ namespace {
&& pos.non_pawn_material() == 2 * BishopValueMg)
sf = 16 + 4 * pe->passed_count();
else
sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);
sf = std::min(sf, 36 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide));
sf = std::max(0, sf - (pos.rule50_count() - 12) / 4 );
}
return ScaleFactor(sf);