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Simplify risk_tolerance + avoid overflow

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passed simplification STC:
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 73984 W: 19058 L: 18879 D: 36047
Ptnml(0-2): 232, 8735, 18866, 8940, 219
https://tests.stockfishchess.org/tests/view/67c269a38200cf1034c9baf9

passed simplification LTC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 39288 W: 10033 L: 9833 D: 19422
Ptnml(0-2): 14, 4168, 11086, 4356, 20
https://tests.stockfishchess.org/tests/view/67c34f8c8200cf1034c9bda1

closes https://github.com/official-stockfish/Stockfish/pull/5919

Bench: 2050046
This commit is contained in:
Carlos Esparza
2025-02-28 17:54:46 -08:00
committed by Disservin
parent b825ea6e57
commit e407a4f269
1 changed files with 12 additions and 11 deletions
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23
src/search.cpp
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@@ -28,6 +28,7 @@
#include <cstdlib>
#include <initializer_list>
#include <iostream>
#include <limits>
#include <list>
#include <ratio>
#include <string>
@@ -99,28 +100,28 @@ int correction_value(const Worker& w, const Position& pos, const Stack* const ss
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 -355752 * x / (x * x + 3 * y * y);
return 644800 * x / ((x * x + 3 * y * y) * y);
};
int material = (67 * pos.count<PAWN>() + 182 * pos.count<KNIGHT>() + 182 * pos.count<BISHOP>()
+ 337 * pos.count<ROOK>() + 553 * pos.count<QUEEN>())
/ 64;
int m = std::clamp(material, 17, 78);
int m = (67 * pos.count<PAWN>() + 182 * pos.count<KNIGHT>() + 182 * pos.count<BISHOP>()
+ 337 * pos.count<ROOK>() + 553 * pos.count<QUEEN>())
/ 64;
// 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 * 3037 / 256 + 2270) * m / 256 - 637) * m / 256 + 413;
int b = ((m * 7936 / 256 - 2255) * m / 256 + 319) * m / 256 + 83;
int a = 356;
int b = ((65 * m - 3172) * m + 240578) / 2048;
// guard against overflow
assert(abs(v) + a <= std::numeric_limits<int>::max() / 644800);
// 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);
int losing_risk = sigmoid_d2(v + a, b);
return (winning_risk + losing_risk) * 58 / b;
return -(winning_risk + losing_risk) * 32;
}
// Add correctionHistory value to raw staticEval and guarantee evaluation
@@ -1192,7 +1193,7 @@ moves_loop: // When in check, search starts here
r -= std::abs(correctionValue) / 29696;
if (PvNode && !is_decisive(bestValue))
if (PvNode && std::abs(bestValue) <= 2000)
r -= risk_tolerance(pos, bestValue);
// Increase reduction for cut nodes