Tune search parameters (with Unai Corzo)

The values used in this patch are taken from a SPSA parameter tuning session
originated by Unai Corzo (@unaiic), but the final difference of his tune was
multiplied x2 by hand. Most of the credits should go to him :-)

STC:
https://tests.stockfishchess.org/tests/view/602f03d07f517a561bc49d40
LLR: 2.94 (-2.94,2.94) {-0.25,1.25}
Total: 67664 W: 6252 L: 6035 D: 55377
Ptnml(0-2): 256, 4799, 23527, 4972, 278

LTC:
https://tests.stockfishchess.org/tests/view/602f41697f517a561bc49d5a
LLR: 2.96 (-2.94,2.94) {0.25,1.25}
Total: 26256 W: 1034 L: 906 D: 24316
Ptnml(0-2): 10, 804, 11377, 922, 15

Closes https://github.com/official-stockfish/Stockfish/pull/3363

Bench: 3957653

diff --git a/src/search.cpp b/src/search.cpp
index b5d21b9d5585c2cfbeed24a6470f9df69c8aa907..8f01f785a9e6596c1999289747ccfbdcb4038660 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -839,7 +839,7 @@ namespace {
     // Step 8. Null move search with verification search (~40 Elo)
     if (   !PvNode
         && (ss-1)->currentMove != MOVE_NULL
-        && (ss-1)->statScore < 22661
+        && (ss-1)->statScore < 24185
         &&  eval >= beta
         &&  eval >= ss->staticEval
         &&  ss->staticEval >= beta - 24 * depth - 34 * improving + 162 * ss->ttPv + 159
@@ -1075,7 +1075,7 @@ moves_loop: // When in check, search starts from here
                   &&  (*contHist[0])[movedPiece][to_sq(move)]
                     + (*contHist[1])[movedPiece][to_sq(move)]
                     + (*contHist[3])[movedPiece][to_sq(move)]
-                    + (*contHist[5])[movedPiece][to_sq(move)] / 3 < 26237)
+                    + (*contHist[5])[movedPiece][to_sq(move)] / 3 < 28255)
                   continue;
 
               // Prune moves with negative SEE (~20 Elo)
@@ -1167,7 +1167,7 @@ moves_loop: // When in check, search starts from here
               || moveCountPruning
               || ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
               || cutNode
-              || (!PvNode && !formerPv && captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 4506)
+              || (!PvNode && !formerPv && captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 3678)
               || thisThread->ttHitAverage < 432 * TtHitAverageResolution * TtHitAverageWindow / 1024))
       {
           Depth r = reduction(improving, depth, moveCount);
@@ -1232,7 +1232,7 @@ moves_loop: // When in check, search starts from here
                              + (*contHist[0])[movedPiece][to_sq(move)]
                              + (*contHist[1])[movedPiece][to_sq(move)]
                              + (*contHist[3])[movedPiece][to_sq(move)]
-                             - 5337;
+                             - 4741;
 
               // Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
               if (ss->statScore >= -89 && (ss-1)->statScore < -116)
@@ -1246,9 +1246,9 @@ moves_loop: // When in check, search starts from here
               // use sum of main history and first continuation history with an offset
               if (ss->inCheck)
                   r -= (thisThread->mainHistory[us][from_to(move)]
-                     + (*contHist[0])[movedPiece][to_sq(move)] - 4341) / 16384;
+                     + (*contHist[0])[movedPiece][to_sq(move)] - 3833) / 16384;
               else
-                  r -= ss->statScore / 14382;
+                  r -= ss->statScore / 14790;
           }
 
           Depth d = std::clamp(newDepth - r, 1, newDepth);