Tweak initiative formula

snicolet · zamar · commit c1be0c68c787 · 2016-03-02T00:02:03.000Z
Give more weight to the pawns number and the vertical king distance in evaluate_initiative() Passed STC: LLR: 2.96 (-2.94,2.94) [0.00,5.00] Total: 26729 W: 5067 L: 4825 D: 16837 and LTC: LLR: 2.95 (-2.94,2.94) [0.00,5.00] Total: 60480 W: 8338 L: 8016 D: 44126 Bench: 8295162 Resolves #594
diff --git a/src/evaluate.cpp b/src/evaluate.cpp
@@ -679,11 +679,12 @@ namespace {
   // status of the players.
   Score evaluate_initiative(const Position& pos, int asymmetry, Value eg) {
 
-    int kingDistance = distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
+    int kingDistance =   distance<File>(pos.square<KING>(WHITE), pos.square<KING>(BLACK))
+                       - distance<Rank>(pos.square<KING>(WHITE), pos.square<KING>(BLACK));
     int pawns = pos.count<PAWN>(WHITE) + pos.count<PAWN>(BLACK);
 
     // Compute the initiative bonus for the attacking side
-    int initiative = 8 * (pawns + asymmetry + kingDistance - 15);
+    int initiative = 8 * (asymmetry + kingDistance) + 12 * pawns - 120;
 
     // Now apply the bonus: note that we find the attacking side by extracting
     // the sign of the endgame value, and that we carefully cap the bonus so
