Tuned Futility Equation
@Vizvezdenec array suggested that alternate values may be better than current
master (see pull request #2270 ). I tuned some linear equations to more closely
represent his values and it passed. These futility values seem quite sensitive,
so perhaps additional Elo improvements can be found here.
STC
LLR: 2.95 (-2.94,2.94) [0.50,4.50]
Total: 12257 W: 2820 L: 2595 D: 6842
http://tests.stockfishchess.org/tests/view/5d5b2f360ebc5925cf1111ac
LTC
LLR: 2.96 (-2.94,2.94) [0.00,3.50]
Total: 20273 W: 3497 L: 3264 D: 13512
http://tests.stockfishchess.org/tests/view/5d5c0d250ebc5925cf111ac3
Closes https://github.com/official-stockfish/Stockfish/pull/2272
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How to continue from there ?
a) we can try a simpler version for the futility margin, this would
be a simplification :
margin = 188 * (depth - improving)
b) on the other direction, we can try a complexification by trying
again to gain Elo with an complete array of futility values.
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Bench: 4330402