Big search tuning

Vizvezdenec · vondele · commit b0b31558a236 · 2022-02-09T17:17:00.000+01:00
Most credits for this patch should go to @candirufish. Based on his big search tuning (1M games at 20+0.1s) https://tests.stockfishchess.org/tests/view/61fc7a6ed508ec6a1c9f4b7d with some hand polishing on top of it, which includes : a) correcting trend sigmoid - for some reason original tuning resulted in it being negative. This heuristic was proven to be worth some elo for years so reversing it sign is probably some random artefact; b) remove changes to continuation history based pruning - this heuristic historically was really good at providing green STCs and then failing at LTC miserably if we tried to make it more strict, original tuning was done at short time control and thus it became more strict - which doesn't scale to longer time controls; c) remove changes to improvement - not really indended :). passed STC https://tests.stockfishchess.org/tests/view/6203526e88ae2c84271c2ee2 LLR: 2.94 (-2.94,2.94) <0.00,2.50> Total: 16840 W: 4604 L: 4363 D: 7873 Ptnml(0-2): 82, 1780, 4449, 2033, 76 passed LTC https://tests.stockfishchess.org/tests/view/620376e888ae2c84271c35d4 LLR: 2.96 (-2.94,2.94) <0.50,3.00> Total: 17232 W: 4771 L: 4542 D: 7919 Ptnml(0-2): 14, 1655, 5048, 1886, 13 closes #3926 bench 5030992
diff --git a/src/search.cpp b/src/search.cpp
@@ -63,15 +63,15 @@ namespace {
 
   // Futility margin
   Value futility_margin(Depth d, bool improving) {
-    return Value(214 * (d - improving));
+    return Value(171 * (d - improving));
   }
 
   // Reductions lookup table, initialized at startup
   int Reductions[MAX_MOVES]; // [depth or moveNumber]
 
   Depth reduction(bool i, Depth d, int mn, Value delta, Value rootDelta) {
     int r = Reductions[d] * Reductions[mn];
-    return (r + 1358 - int(delta) * 1024 / int(rootDelta)) / 1024 + (!i && r > 904);
+    return (r + 1575 - int(delta) * 1024 / int(rootDelta)) / 1024 + (!i && r > 1011);
   }
 
   constexpr int futility_move_count(bool improving, Depth depth) {
@@ -80,7 +80,7 @@ namespace {
 
   // History and stats update bonus, based on depth
   int stat_bonus(Depth d) {
-    return std::min((6 * d + 229) * d - 215 , 2000);
+    return std::min((7 * d + 254) * d - 206 , 1990);
   }
 
   // Add a small random component to draw evaluations to avoid 3-fold blindness
@@ -157,7 +157,7 @@ namespace {
 void Search::init() {
 
   for (int i = 1; i < MAX_MOVES; ++i)
-      Reductions[i] = int((21.9 + std::log(Threads.size()) / 2) * std::log(i));
+      Reductions[i] = int((21.5 + std::log(Threads.size()) / 2) * std::log(i));
 }
 
 
@@ -303,10 +303,10 @@ void Thread::search() {
 
   multiPV = std::min(multiPV, rootMoves.size());
 
-  complexityAverage.set(232, 1);
+  complexityAverage.set(190, 1);
 
   trend         = SCORE_ZERO;
-  optimism[ us] = Value(25);
+  optimism[ us] = Value(34);
   optimism[~us] = -optimism[us];
 
   int searchAgainCounter = 0;
@@ -349,16 +349,16 @@ void Thread::search() {
           if (rootDepth >= 4)
           {
               Value prev = rootMoves[pvIdx].averageScore;
-              delta = Value(17) + int(prev) * prev / 16384;
+              delta = Value(16) + int(prev) * prev / 16384;
               alpha = std::max(prev - delta,-VALUE_INFINITE);
               beta  = std::min(prev + delta, VALUE_INFINITE);
 
               // Adjust trend and optimism based on root move's previousScore
-              int tr = sigmoid(prev, 0, 0, 147, 113, 1);
+              int tr = sigmoid(prev, 6, 13, 96, 110, 1);
               trend = (us == WHITE ?  make_score(tr, tr / 2)
                                    : -make_score(tr, tr / 2));
 
-              int opt = sigmoid(prev, 0, 25, 147, 14464, 256);
+              int opt = sigmoid(prev, 7, 21, 94, 14786, 221);
               optimism[ us] = Value(opt);
               optimism[~us] = -optimism[us];
           }
@@ -413,7 +413,7 @@ void Thread::search() {
               else
                   break;
 
-              delta += delta / 4 + 5;
+              delta += delta / 4 + 3;
 
               assert(alpha >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
           }
@@ -459,17 +459,17 @@ void Thread::search() {
           && !Threads.stop
           && !mainThread->stopOnPonderhit)
       {
-          double fallingEval = (142 + 12 * (mainThread->bestPreviousAverageScore - bestValue)
-                                    +  6 * (mainThread->iterValue[iterIdx] - bestValue)) / 825.0;
+          double fallingEval = (87 + 12 * (mainThread->bestPreviousAverageScore - bestValue)
+                                    +  6 * (mainThread->iterValue[iterIdx] - bestValue)) / 777.20;
           fallingEval = std::clamp(fallingEval, 0.5, 1.5);
 
           // If the bestMove is stable over several iterations, reduce time accordingly
-          timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.92 : 0.95;
-          double reduction = (1.47 + mainThread->previousTimeReduction) / (2.32 * timeReduction);
+          timeReduction = lastBestMoveDepth + 8 < completedDepth ? 1.70 : 0.91;
+          double reduction = (1.59 + mainThread->previousTimeReduction) / (2.33 * timeReduction);
           double bestMoveInstability = 1.073 + std::max(1.0, 2.25 - 9.9 / rootDepth)
                                               * totBestMoveChanges / Threads.size();
           int complexity = mainThread->complexityAverage.value();
-          double complexPosition = std::clamp(1.0 + (complexity - 232) / 1750.0, 0.5, 1.5);
+          double complexPosition = std::clamp(1.0 + (complexity - 312) / 1750.0, 0.5, 1.5);
 
           double totalTime = Time.optimum() * fallingEval * reduction * bestMoveInstability * complexPosition;
 
@@ -490,7 +490,7 @@ void Thread::search() {
           }
           else if (   Threads.increaseDepth
                    && !mainThread->ponder
-                   && Time.elapsed() > totalTime * 0.58)
+                   && Time.elapsed() > totalTime * 0.55)
                    Threads.increaseDepth = false;
           else
                    Threads.increaseDepth = true;
@@ -788,19 +788,19 @@ namespace {
     // Step 8. Futility pruning: child node (~25 Elo).
     // The depth condition is important for mate finding.
     if (   !ss->ttPv
-        &&  depth < 9
+        &&  depth < 8
         &&  eval - futility_margin(depth, improving) - (ss-1)->statScore / 256 >= beta
         &&  eval >= beta
-        &&  eval < 15000) // 50% larger than VALUE_KNOWN_WIN, but smaller than TB wins.
+        &&  eval < 17548) // 50% larger than VALUE_KNOWN_WIN, but smaller than TB wins.
         return eval;
 
     // Step 9. Null move search with verification search (~22 Elo)
     if (   !PvNode
         && (ss-1)->currentMove != MOVE_NULL
-        && (ss-1)->statScore < 23767
+        && (ss-1)->statScore < 13706
         &&  eval >= beta
         &&  eval >= ss->staticEval
-        &&  ss->staticEval >= beta - 20 * depth - improvement / 15 + 204 + complexity / 25
+        &&  ss->staticEval >= beta - 19 * depth - improvement / 15 + 200 + complexity / 25
         && !excludedMove
         &&  pos.non_pawn_material(us)
         && (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
@@ -844,13 +844,13 @@ namespace {
         }
     }
 
-    probCutBeta = beta + 209 - 44 * improving;
+    probCutBeta = beta + 229 - 47 * improving;
 
     // Step 10. ProbCut (~4 Elo)
     // If we have a good enough capture and a reduced search returns a value
     // much above beta, we can (almost) safely prune the previous move.
     if (   !PvNode
-        &&  depth > 4
+        &&  depth > 3
         &&  abs(beta) < VALUE_TB_WIN_IN_MAX_PLY
         // if value from transposition table is lower than probCutBeta, don't attempt probCut
         // there and in further interactions with transposition table cutoff depth is set to depth - 3
@@ -871,7 +871,6 @@ namespace {
             if (move != excludedMove && pos.legal(move))
             {
                 assert(pos.capture_or_promotion(move));
-                assert(depth >= 5);
 
                 captureOrPromotion = true;
 
@@ -909,19 +908,19 @@ namespace {
 
     // Step 11. If the position is not in TT, decrease depth by 2 or 1 depending on node type (~3 Elo)
     if (   PvNode
-        && depth >= 6
+        && depth >= 4
         && !ttMove)
         depth -= 2;
 
     if (   cutNode
-        && depth >= 9
+        && depth >= 7
         && !ttMove)
         depth--;
 
 moves_loop: // When in check, search starts here
 
     // Step 12. A small Probcut idea, when we are in check (~0 Elo)
-    probCutBeta = beta + 409;
+    probCutBeta = beta + 401;
     if (   ss->inCheck
         && !PvNode
         && depth >= 4
@@ -1017,12 +1016,12 @@ namespace {
                   && !PvNode
                   && lmrDepth < 6
                   && !ss->inCheck
-                  && ss->staticEval + 342 + 238 * lmrDepth + PieceValue[EG][pos.piece_on(to_sq(move))]
+                  && ss->staticEval + 392 + 207 * lmrDepth + PieceValue[EG][pos.piece_on(to_sq(move))]
                    + captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 8 < alpha)
                   continue;
 
               // SEE based pruning (~9 Elo)
-              if (!pos.see_ge(move, Value(-217) * depth))
+              if (!pos.see_ge(move, Value(-200) * depth))
                   continue;
           }
           else
@@ -1040,12 +1039,12 @@ namespace {
 
               // Futility pruning: parent node (~9 Elo)
               if (   !ss->inCheck
-                  && lmrDepth < 8
-                  && ss->staticEval + 138 + 137 * lmrDepth + history / 64 <= alpha)
+                  && lmrDepth < 11
+                  && ss->staticEval + 131 + 137 * lmrDepth + history / 64 <= alpha)
                   continue;
 
               // Prune moves with negative SEE (~3 Elo)
-              if (!pos.see_ge(move, Value(-21 * lmrDepth * lmrDepth - 21 * lmrDepth)))
+              if (!pos.see_ge(move, Value(-25 * lmrDepth * lmrDepth - 29 * lmrDepth)))
                   continue;
           }
       }
@@ -1081,7 +1080,7 @@ namespace {
 
                   // Avoid search explosion by limiting the number of double extensions
                   if (  !PvNode
-                      && value < singularBeta - 75
+                      && value < singularBeta - 71
                       && ss->doubleExtensions <= 6)
                       extension = 2;
               }
@@ -1101,15 +1100,15 @@ namespace {
 
           // Check extensions (~1 Elo)
           else if (   givesCheck
-                   && depth > 6
-                   && abs(ss->staticEval) > 100)
+                   && depth > 7
+                   && abs(ss->staticEval) > 128)
               extension = 1;
 
           // Quiet ttMove extensions (~0 Elo)
           else if (   PvNode
                    && move == ttMove
                    && move == ss->killers[0]
-                   && (*contHist[0])[movedPiece][to_sq(move)] >= 10000)
+                   && (*contHist[0])[movedPiece][to_sq(move)] >= 8932)
               extension = 1;
       }
 
@@ -1136,8 +1135,8 @@ namespace {
       // We use various heuristics for the sons of a node after the first son has
       // been searched. In general we would like to reduce them, but there are many
       // cases where we extend a son if it has good chances to be "interesting".
-      if (    depth >= 3
-          &&  moveCount > 1 + 2 * rootNode
+      if (    depth >= 2
+          &&  moveCount > 1 + rootNode
           && (   !ss->ttPv
               || !captureOrPromotion
               || (cutNode && (ss-1)->moveCount > 1)))
@@ -1146,7 +1145,7 @@ namespace {
 
           // Decrease reduction at some PvNodes (~2 Elo)
           if (   PvNode
-              && bestMoveCount <= 3)
+              && bestMoveCount <= 4)
               r--;
 
           // Decrease reduction if position is or has been on the PV
@@ -1156,7 +1155,7 @@ namespace {
               r -= 2;
 
           // Decrease reduction if opponent's move count is high (~1 Elo)
-          if ((ss-1)->moveCount > 13)
+          if ((ss-1)->moveCount > 7)
               r--;
 
           // Increase reduction for cut nodes (~3 Elo)
@@ -1171,18 +1170,18 @@ namespace {
                          + (*contHist[0])[movedPiece][to_sq(move)]
                          + (*contHist[1])[movedPiece][to_sq(move)]
                          + (*contHist[3])[movedPiece][to_sq(move)]
-                         - 4923;
+                         - 4142;
 
           // Decrease/increase reduction for moves with a good/bad history (~30 Elo)
-          r -= ss->statScore / 14721;
+          r -= ss->statScore / 15328;
 
           // In general we want to cap the LMR depth search at newDepth. But if reductions
           // are really negative and movecount is low, we allow this move to be searched
           // deeper than the first move (this may lead to hidden double extensions).
           int deeper =   r >= -1                   ? 0
                        : moveCount <= 5            ? 2
-                       : PvNode && depth > 6       ? 1
-                       : cutNode && moveCount <= 7 ? 1
+                       : PvNode && depth > 4       ? 1
+                       : cutNode && moveCount <= 5 ? 1
                        :                             0;
 
           Depth d = std::clamp(newDepth - r, 1, newDepth + deeper);
@@ -1191,7 +1190,7 @@ namespace {
 
           // If the son is reduced and fails high it will be re-searched at full depth
           doFullDepthSearch = value > alpha && d < newDepth;
-          doDeeperSearch = value > (alpha + 62 + 20 * (newDepth - d));
+          doDeeperSearch = value > (alpha + 80 + 20 * (newDepth - d));
           didLMR = true;
       }
       else
@@ -1212,7 +1211,7 @@ namespace {
                                         : -stat_bonus(newDepth);
 
               if (captureOrPromotion)
-                  bonus /= 4;
+                  bonus /= 5;
 
               update_continuation_histories(ss, movedPiece, to_sq(move), bonus);
           }
@@ -1343,7 +1342,7 @@ namespace {
         //or fail low was really bad
         bool extraBonus =    PvNode
                           || cutNode
-                          || bestValue < alpha - 94 * depth;
+                          || bestValue < alpha - 99 * depth;
 
         update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth) * (1 + extraBonus));
     }
@@ -1474,7 +1473,7 @@ namespace {
         if (PvNode && bestValue > alpha)
             alpha = bestValue;
 
-        futilityBase = bestValue + 155;
+        futilityBase = bestValue + 127;
     }
 
     const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
