Scale down endgame factor when shuffling

snicolet · snicolet · commit 7b064752943b · 2019-09-16T01:37:39.000+02:00
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: #2304 Bench: 4272173
diff --git a/src/evaluate.cpp b/src/evaluate.cpp
@@ -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);

Original file line number	Diff line number	Diff line change
`@@ -769,8 +769,9 @@ namespace {`
`769`	`769`	`&& pos.non_pawn_material() == 2 * BishopValueMg)`
`770`	`770`	`sf = 16 + 4 * pe->passed_count();`
`771`	`771`	`else`
`772`		`- sf = std::min(40 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide), sf);`
	`772`	`+ sf = std::min(sf, 36 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide));`
`773`	`773`
	`774`	`+ sf = std::max(0, sf - (pos.rule50_count() - 12) / 4 );`
`774`	`775`	`}`
`775`	`776`
`776`	`777`	`return ScaleFactor(sf);`