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Simplification: use Arctan for the optimism S-curve

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This was an idea of Gontran Lemaire (gonlem), but the graphs
he published did not seem accurate to me. I did my own graphs,
got my own constants and here is the result:

STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 42179 W: 8704 L: 8622 D: 24853
http://tests.stockfishchess.org/tests/view/5a9db6270ebc590297cb611b

LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 17737 W: 2702 L: 2577 D: 12458
http://tests.stockfishchess.org/tests/view/5a9eb5b20ebc590297cb61b2

Note: we are now back to 70% draw rate in selfplay mode!

Bench: 5544908
This commit is contained in:
IIvec 2018-03-05 22:24:26 +01:00 • committed by Stéphane Nicolet
parent 65c3bb8586
commit 82697f1193
1 changed files with 1 additions and 4 deletions
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5
src/search.cpp
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@ -351,10 +351,7 @@ void Thread::search() {
ct = Options["Contempt"] * PawnValueEg / 100; // From centipawns
// Adjust contempt based on current bestValue (dynamic contempt)
int sign = (bestValue > 0) - (bestValue < 0);
ct += bestValue > 500 ? 70 :
bestValue < -500 ? -70 :
bestValue / 10 + sign * int(std::round(3.22 * log(1 + abs(bestValue))));
ct += int(std::round(48 * atan(float(bestValue) / 128)));
Eval::Contempt = (us == WHITE ? make_score(ct, ct / 2)
: -make_score(ct, ct / 2));