From 7e9b131efb832339ee6cd9e22b7c837c3e69a1b5 Mon Sep 17 00:00:00 2001
From: windfishballad <windfishballadtcec@gmail.com>
Date: Mon, 22 May 2023 20:13:44 -0400
Subject: [PATCH] Removed quadratic term in optimism

Remove term which is quadratic in optimism in the eval.
Simplifies and should also remove the bias towards side to move making the eval better for analysis.

STC: https://tests.stockfishchess.org/tests/view/6470a9d8c29e0d4352b0bca5
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 154432 W: 41127 L: 41040 D: 72265
Ptnml(0-2): 380, 17094, 42190, 17163, 389

LTC: https://tests.stockfishchess.org/tests/view/6471e9b3e549d9cf2fb219ef
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 127926 W: 34474 L: 34369 D: 59083
Ptnml(0-2): 43, 12505, 38776, 12582, 57

closes https://github.com/official-stockfish/Stockfish/pull/4590

Bench: 2541211
---
 AUTHORS          | 1 +
 src/evaluate.cpp | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/AUTHORS b/AUTHORS
index 884bffab..d01d23cd 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -213,6 +213,7 @@ tttak
 Unai Corzo (unaiic)
 Uri Blass (uriblass)
 Vince Negri (cuddlestmonkey)
+windfishballad
 xefoci7612
 zz4032
 
diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index cc789e35..7239fd1e 100644
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -1072,7 +1072,7 @@ Value Eval::evaluate(const Position& pos) {
 
       // Blend nnue complexity with (semi)classical complexity
       nnueComplexity = (  397 * nnueComplexity
-                        + (477 + optimism) * abs(psq - nnue)
+                        + 477 * abs(psq - nnue)
                         ) / 1024;
 
       optimism += optimism * nnueComplexity / 256;
-- 
2.39.2