We calculate tropism as a sum of two factors. The first is the number of squares in our kingFlank and Camp that are attacked by the enemy; the second is number of these squares that are attacked twice. Prior to this commit, we excluded squares we defended with pawns from this second value, but this appears unnecessary. (Doubly-attacked squares near our king are still dangerous.) The removal of this exclusion is a possible small Elo gain at STC (estimated +1.59) and almost exactly neutral at LTC (estimated +0.04).
STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 20942 W: 4550 L: 4427 D: 11965
http://tests.stockfishchess.org/tests/view/5be4e0ae0ebc595e0ae308a0
LTC:
LLR: 2.94 (-2.94,2.94) [-3.00,1.00]
Total: 56941 W: 9172 L: 9108 D: 38661
http://tests.stockfishchess.org/tests/view/5be4ec340ebc595e0ae30938
Bench: 3813986
This PR is a combination of two unrelated [0, 4] patches that appeared promising
but not quite strong enough to pass on their own. The combination initially failed
STC with a positive score after a long run, and the subsequent speculative LTC test
passed.
* tweak_threatOnQueen4 :
Increase the middlegame components of ThreatByMinor[QUEEN]
and ThreatByRook[QUEEN] by 15 each. Bryan's (@crossbr) analysis of CCC Bonus Game 10
inspired several tests on penalizing a queen with limited safe mobility. While
attempting to implement this idea, I noticed that when I did not include the queen's
current square in the calculations, the Elo gains seemed to vanish--and only then did
I have the idea to revisit ThreatByMinor[QUEEN] and ThreatByRook[QUEEN], adding a
corresponding value to each. Without Bryan's work, this test would never have been
submitted. I would also like to recognize the efforts and contributions of @SFisGOD,
who also vigorously worked on this idea.
* Use pure static eval for null move pruning :
This idea was directly re-purposed from a promising test by Jerry Donald Watson
(@jerrydonaldwatson) in August. It was also independently developed and tested by
Stefan Geschwentner (@locutus2) previously.
Thank you all!
STC (failed yellow):
LLR: -2.96 (-2.94,2.94) [0.00,4.00]
Total: 83913 W: 17986 L: 17825 D: 48102
http://tests.stockfishchess.org/tests/view/5bbc59300ebc592439f76aa5
LTC:
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 137198 W: 22351 L: 21772 D: 93075
http://tests.stockfishchess.org/tests/view/5bbce35f0ebc592439f77639
Bench: 4312846
In the current master, ThreatByKing is an array of two Scores, one for
when we have a single attack and one for when we have many. The latter
case is very rarely called during bench and was recently given a strange
negative value during a tuning run, as pointed out by @candirufish on
commit efd4ca2. Here, we simplify away this second case entirely, and
increase the remaining ThreatByKing to compensate.
Although I derived the parameter tweak independently, with the goal of
preserving the same average bonus, I later noticed that a very similar
Score had already been derived by an ongoing SPSA tuning session.
I therefore recognize @candirufish for first discovering these values.
I would also like to thank @Rocky640 for valuable feedback that pointed
me in the direction of ThreatByKing.
STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 7677 W: 1772 L: 1623 D: 4282
http://tests.stockfishchess.org/tests/view/5b3db0320ebc5902b9ffe97a
LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 108031 W: 18329 L: 18350 D: 71352
http://tests.stockfishchess.org/tests/view/5b3dbf4b0ebc5902b9ffe9db
Closes https://github.com/official-stockfish/Stockfish/pull/1666
Bench: 4678861
