Remove the tropism term from kingDanger

A recent LTC tuning session by @candirufish showed this term decreasing significantly. It appears that it can be removed altogether without significant Elo loss.

I also thank @GuardianRM, whose attempt to remove tropism from king danger inspired this one.

After this PR is merged, my next step will be to attempt to tune the coefficients of this new, simplified kingDanger calculation.

STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 12518 W: 2795 L: 2656 D: 7067
http://tests.stockfishchess.org/tests/view/5befadda0ebc595e0ae3a289

LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 164771 W: 26463 L: 26566 D: 111742
http://tests.stockfishchess.org/tests/view/5befcca70ebc595e0ae3a343

LTC 2, rebased on Stockfish 10 beta:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 75226 W: 12563 L: 12529 D: 50134
http://tests.stockfishchess.org/tests/view/5bf2e8910ebc5902bcecb919

Bench: 3412071

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index f2126512413f576417faaed3bb08db28419afb3d..e5e3cb6ccbe6d0f1029d72b51228e95920ea1514 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -475,7 +475,6 @@ namespace {
                      +  69 * kingAttacksCount[Them]
                      + 185 * popcount(kingRing[Us] & weak)
                      + 150 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
-                     +   4 * tropism
                      - 873 * !pos.count<QUEEN>(Them)
                      -   6 * mg_value(score) / 8
                      +       mg_value(mobility[Them] - mobility[Us])