diff --git a/src/uci.cpp b/src/uci.cpp index 8dd485b0..e28dba32 100644 --- a/src/uci.cpp +++ b/src/uci.cpp @@ -222,6 +222,28 @@ namespace { << "\nNodes/second : " << 1000 * nodes / elapsed << endl; } + // The win rate model returns the probability (per mille) of winning given an eval + // and a game-ply. The model fits rather accurately the LTC fishtest statistics. + int win_rate_model(Value v, int ply) { + + // The model captures only up to 240 plies, so limit input (and rescale) + double m = std::min(240, ply) / 64.0; + + // Coefficients of a 3rd order polynomial fit based on fishtest data + // for two parameters needed to transform eval to the argument of a + // logistic function. + double as[] = {-8.24404295, 64.23892342, -95.73056462, 153.86478679}; + double bs[] = {-3.37154371, 28.44489198, -56.67657741, 72.05858751}; + double a = (((as[0] * m + as[1]) * m + as[2]) * m) + as[3]; + double b = (((bs[0] * m + bs[1]) * m + bs[2]) * m) + bs[3]; + + // Transform eval to centipawns with limited range + double x = Utility::clamp(double(100 * v) / PawnValueEg, -1000.0, 1000.0); + + // Return win rate in per mille (rounded to nearest) + return int(0.5 + 1000 / (1 + std::exp((a - x) / b))); + } + // When you calculate check sum, save it and check the consistency later. uint64_t eval_sum; } // namespace