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Commit ID 87ed9facf16bc9d0af9daf8680801759ce1d8662
Author 31m059
Date 2019-11-23 23:34:43 UTC
King danger: retire attacked-by-bishop defense In a recent commit, "Introduce king flank defenders," a term was introduced by Michael Chaly (@Vizvezdenec) to reduce king danger based on king defenders, i.e., friendly attacks on our King Flank and Camp. This is a powerful idea and broadly applicable to all of our pieces. An earlier, but narrower, version of a similar idea was already coded into king danger, with a term reducing king danger simply if we had a bishop and king attacking the same square -- there is also a similar term for knights, but roughly three times larger. I had attempted to tweak this term's coefficient fairly recently, in a series of tests in early September which increased this coefficient. All failed STC with significantly negative scores. Now that the king flank defenders term has been introduced, it appears that the bishop-defense term can be simplified away without compensation or significant Elo loss. Where do we go from here? This PR is a natural follow-up to "Introduce king flank defenders," which proposed simplification with existing and overlapping terms, such as this one. That PR also mentioned that the coefficient it introduced appeared arbitrary, so perhaps this PR can facilitate a tweak to increase king flank defenders' coefficient. Additionally, this pull request is extremely similar to, which was (coincidentally) merged a year ago, to the day (November 23, 2018). That patch also simplified away a linear king danger tropism term, which was soon after replaced with a quadratic term by @Vizvezdenec (which would not have passed without the simplification). @Vizvezdenec, again by coincidence, has recently been trying to implement a quadratic term, this time for defenders rather than attackers. This history of this evaluation code suggests that this simplification might be enough to help a patch for quadratic king-flank defenders pass. Bench: 4959670 STC: LLR: 2.94 (-2.94,2.94) [-3.00,1.00] Total: 22209 W: 4920 L: 4800 D: 12489 LTC: LLR: 2.95 (-2.94,2.94) [-3.00,1.00] Total: 152107 W: 24658 L: 24743 D: 102706 Interesting discussion on Github about this pull request: --- This pull request was opened less than one week before the holiday of Thanksgiving here in the United States. In keeping with the holiday tradition of expressing gratitude, I would like to thank our generous CPU donors, talented forum contributors, innovative developers, speedy fishtest approvers, and especially our hardworking server maintainers (@ppigazzini and @tomtor). Thank you all for a year of great Stockfish progress!
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