Double weight of pawn history for quiet move ordering.

I measured on my 1000 position bench the average additional added pawn history per depth.
This shows on average negative value with even smaller values with increaing depth.

A linear regression against depth get following formula:

-1960 - 130 * depth

For compensation add this to the used sort limit to maintain roughly the same proportion of sorted quiet moves.

Remarks:
1. using no compensation failed here https://tests.stockfishchess.org/tests/view/6547664f136acbc5735265f0
2. using only the compensation failed at LTC:
   passed STC: https://tests.stockfishchess.org/tests/view/65477457136acbc5735266f8
   failed LTC: https://tests.stockfishchess.org/tests/view/65487fc8136acbc573527d1c

STC:
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 98528 W: 25109 L: 24699 D: 48720
Ptnml(0-2): 334, 11586, 25009, 12006, 329
https://tests.stockfishchess.org/tests/view/65475873136acbc5735264f7

LTC:
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 69726 W: 17467 L: 17073 D: 35186
Ptnml(0-2): 39, 7814, 18769, 8196, 45
https://tests.stockfishchess.org/tests/view/6547e759136acbc573527071

closes https://github.com/official-stockfish/Stockfish/pull/4866

Bench: 1379422

diff --git a/src/movepick.cpp b/src/movepick.cpp
index 0aba9a55fe79d5b25d53da9b2e4e3e0f6ca19e1d..798f51ddb6e56d2c5918c6be26ba64d4de8c46ec 100644 (file)
--- a/src/movepick.cpp
+++ b/src/movepick.cpp
@@ -181,12 +181,12 @@ void MovePicker::score() {
 
             // histories
             m.value = 2 * (*mainHistory)[pos.side_to_move()][from_to(m)];
+            m.value += 2 * (*pawnHistory)[pawn_structure(pos)][pc][to];
             m.value += 2 * (*continuationHistory[0])[pc][to];
             m.value += (*continuationHistory[1])[pc][to];
             m.value += (*continuationHistory[2])[pc][to] / 4;
             m.value += (*continuationHistory[3])[pc][to];
             m.value += (*continuationHistory[5])[pc][to];
-            m.value += (*pawnHistory)[pawn_structure(pos)][pc][to];
 
             // bonus for checks
             m.value += bool(pos.check_squares(pt) & to) * 16384;
@@ -302,7 +302,7 @@ top:
             endMoves = generate<QUIETS>(pos, cur);
 
             score<QUIETS>();
-            partial_insertion_sort(cur, endMoves, -3000 * depth);
+            partial_insertion_sort(cur, endMoves, -1960 - 3130 * depth);
         }
 
         ++stage;