Scale down complexity for almost unwinnable endgames
This patch greatly scales down complexity of endgames when the
following conditions are all true together:
- pawns are all on one flank
- stronger side king is not outflanking weaker side
- no passed pawns are present
This should improve stockfish evaluation of obvious draws 4 vs 3, 3 vs 2
and 2 vs 1 pawns in rook/queen/knight/bishop single flank endgames where
strong side can not make progress.
passed STC
LLR: 2.94 (-2.94,2.94) [0.50,4.50]
Total: 15843 W: 3601 L: 3359 D: 8883
passed LTC
LLR: 2.96 (-2.94,2.94) [0.00,3.50]
Total: 121275 W: 20107 L: 19597 D: 81571
Closes https://github.com/official-stockfish/Stockfish/pull/2298
Bench: 3954190
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How to continue from there?
a) This could be a powerful idea for refining some parts of the evaluation
function, a bit like when we try quadratics or other equations to emphasize
certain situations (xoto10).
b) Some other combinaison values for this bonus can be done further, or
overall retuning of weight and offset while keeping the formula simple.