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Add risk tolerance calculation

Browse Source 
https://tests.stockfishchess.org/tests/view/67b1db2188b11e2400eb06ae
Passed STC:
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 123552 W: 32388 L: 31938 D: 59226
Ptnml(0-2): 487, 14520, 31345, 14904, 520

Passed LTC:
https://tests.stockfishchess.org/tests/view/67b3d53f154c4df4fc4b1f43
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 206928 W: 52916 L: 52246 D: 101766
Ptnml(0-2): 159, 22546, 57394, 23196, 169

closes https://github.com/official-stockfish/Stockfish/pull/5893

Bench: 2705449
This commit is contained in:
Myself
2025-02-24 19:12:35 +01:00
committed by Disservin
parent 291a429cdd
commit 57f0fe08c0
1 changed files with 29 additions and 0 deletions
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src/search.cpp
+29
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@@ -96,6 +96,32 @@ int correction_value(const Worker& w, const Position& pos, const Stack* const ss
return 6995 * pcv + 6593 * micv + 7753 * (wnpcv + bnpcv) + 6049 * cntcv;
}
int risk_tolerance(const Position& pos, Value v) {
// Returns (some constant of) second derivative of sigmoid.
static constexpr auto sigmoid_d2 = [](int x, int y) {
return -345600 * x / (x * x + 3 * y * y);
};
int material = pos.count<PAWN>() + 3 * pos.count<KNIGHT>() + 3 * pos.count<BISHOP>()
+ 5 * pos.count<ROOK>() + 9 * pos.count<QUEEN>();
int m = std::clamp(material, 17, 78);
// a and b are the crude approximation of the wdl model.
// The win rate is: 1/(1+exp((a-v)/b))
// The loss rate is 1/(1+exp((v+a)/b))
int a = ((-m * 3220 / 256 + 2361) * m / 256 - 586) * m / 256 + 421;
int b = ((m * 7761 / 256 - 2674) * m / 256 + 314) * m / 256 + 51;
// The risk utility is therefore d/dv^2 (1/(1+exp(-(v-a)/b)) -1/(1+exp(-(-v-a)/b)))
// -115200x/(x^2+3) = -345600(ab) / (a^2+3b^2) (multiplied by some constant) (second degree pade approximant)
int winning_risk = sigmoid_d2(v - a, b);
int losing_risk = -sigmoid_d2(-v - a, b);
return (winning_risk + losing_risk) * 60 / b;
}
// Add correctionHistory value to raw staticEval and guarantee evaluation
// does not hit the tablebase range.
Value to_corrected_static_eval(const Value v, const int cv) {
@@ -1166,6 +1192,9 @@ moves_loop: // When in check, search starts here
r -= std::abs(correctionValue) / 31568;
if (PvNode && !is_decisive(bestValue))
r -= risk_tolerance(pos, bestValue);
// Increase reduction for cut nodes
if (cutNode)
r += 2608 + 1024 * !ttData.move;