Decrease LMR at PV nodes with low depth.

KJE-98 · dav1312 · commit b6b4d6953e00 · 2022-10-21T14:05:01.000+02:00
This patch lessens the Late Move Reduction at PV nodes with low depth. Previously the affect of depth on LMR was independant of nodeType. The idea behind this patch is that at PV nodes, LMR at low depth is will miss out on potential alpha-raising moves. Passed STC: https://tests.stockfishchess.org/tests/view/625aa867d3367522c4b8965c LLR: 2.93 (-2.94,2.94) <0.00,2.50> Total: 19360 W: 5252 L: 5006 D: 9102 Ptnml(0-2): 79, 2113, 5069, 2321, 98 Passed LTC: https://tests.stockfishchess.org/tests/view/625ae844d3367522c4b8a009 LLR: 2.94 (-2.94,2.94) <0.50,3.00> Total: 39264 W: 10636 L: 10357 D: 18271 Ptnml(0-2): 18, 3928, 11473, 4183, 30 closes official-stockfish#3985 bench: 8129754
diff --git a/AUTHORS b/AUTHORS
@@ -104,6 +104,7 @@ jundery
 Justin Blanchard (UncombedCoconut)
 Kelly Wilson
 Ken Takusagawa
+Kian E (KJE-98)
 kinderchocolate
 Kiran Panditrao (Krgp)
 Kojirion
diff --git a/src/search.cpp b/src/search.cpp
@@ -1173,6 +1173,10 @@ namespace {
           if (PvNode && !ss->inCheck && abs(ss->staticEval - bestValue) > 250)
               r--;
 
+          // Increase depth based reduction if PvNode
+          if (PvNode)
+              r -= 15 / ( 3 + depth );
+
           ss->statScore =  thisThread->mainHistory[us][from_to(move)]
                          + (*contHist[0])[movedPiece][to_sq(move)]
                          + (*contHist[1])[movedPiece][to_sq(move)]
