Stockfish evaluates passed pawns in part based on a variable k, which shapes the passed pawn bonus based on the number of squares between the current square and promotion square that are attacked by enemy pieces, and the number defended by friendly ones. Prior to this commit, we gave a large bonus when all squares between the pawn and the promotion square were defended, and if they were not, a somewhat smaller bonus if at least the pawn's next square was. However, this distinction does not appear to provide any Elo at STC or LTC.
Where do we go from here? Many promising Elo-gaining patches were attempted in the past few months to refine passed pawn calculation, by altering the definitions of unsafe and defended squares. Stockfish uses these definitions to choose the value of k, so those tests interact with this PR. Therefore, it may be worthwhile to retest previously promising but not-quite-passing tests in the vicinity of this patch.
STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 42344 W: 9455 L: 9374 D: 23515
http://tests.stockfishchess.org/tests/view/5cf83ede0ebc5925cf0904fb
LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 69548 W: 11855 L: 11813 D: 45880
http://tests.stockfishchess.org/tests/view/5cf8698f0ebc5925cf0908c8
Bench: 3854907
This is a non-functional simplification. Since our file_bb handles either Files or Squares, using Square here removes some code. Not likely any performance difference despite the test.
STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 6081 W: 1444 L: 1291 D: 3346
http://tests.stockfishchess.org/tests/view/5ceb3e2e0ebc5925cf07ab03
Non functional change.
We evaluate defended and unsafe squares for a passed pawn push based on friendly and enemy rooks and queens on the passed pawn's file. Prior to this patch, we further required that these rooks and queens be able to directly attack the passed pawn. However, this restriction appears unnecessary and worth almost exactly 0 Elo at LTC.
The simplified code allows rooks and queens to attack/defend the passed pawn through other pieces of either color.
STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 29019 W: 6488 L: 6381 D: 16150
http://tests.stockfishchess.org/tests/view/5cdcf7270ebc5925cf05d30c
LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 54224 W: 9200 L: 9133 D: 35891
http://tests.stockfishchess.org/tests/view/5cddc6210ebc5925cf05eca3
Bench: 3415326
Same idea as fisherman's knight protection.
passed STC
LLR: 2.96 (-2.94,2.94) [0.50,4.50]
Total: 17133 W: 3952 L: 3701 D: 9480
http://tests.stockfishchess.org/tests/view/5cc3550b0ebc5925cf02dada
passed LTC
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 37316 W: 6470 L: 6188 D: 24658
http://tests.stockfishchess.org/tests/view/5cc3721d0ebc5925cf02dc90
Looking at this 2 ideas being recent clean elo gainers I have a feeling that we can add also rook and queen protection bonuses or overall move this stuff in pieces loop in the same way as we do pieces attacking bonuses on their kingring... :) Thx fisherman for original idea.
Bench 3429173
We can remove the values in Pawns if we just use the piece arrays in Position. This reduces the size of a pawn entry. This simplification passed individually, and in concert with ps_passedcount100 (removes passedCount storage in pawns.).
STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 19957 W: 4529 L: 4404 D: 11024
http://tests.stockfishchess.org/tests/view/5cb3c2d00ebc5925cf016f0d
Combo STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 17368 W: 3925 L: 3795 D: 9648
http://tests.stockfishchess.org/tests/view/5cb3d3510ebc5925cf01709a
This is a non-functional simplification.
The kingDanger term is intended to give a penalty which increases rapidly in the middlegame but less so in the endgame. To this end, the middlegame component is quadratic, and the endgame component is linear. However, this produces unintended consequences for relatively small values of kingDanger: the endgame penalty will exceed the middlegame penalty. This remains true up to kingDanger = 256 (a S(16, 16) penalty), so some of these inaccurate penalties are actually rather large.
In this patch, we increase the threshold for applying the kingDanger penalty to eliminate some of this unintended behavior. This was very nearly, but not quite, sufficient to pass on its own. The patch was finally successful by integrating a second kingDanger tweak by @Vizvezdenec, increasing the kingDanger constant term slightly and improving both STC and LTC performance.
Where do we go from here? I propose that in the future, any attempts to tune kingDanger coefficients should also consider tuning the kingDanger threshold. The evidence shows clearly that it should not be automatically taken to be zero.
Special thanks to @Vizvezdenec for the kingDanger constant tweak. Thanks also to all the approvers and CPU donors who made this possible!
STC:
LLR: -2.96 (-2.94,2.94) [0.00,4.00]
Total: 141225 W: 31239 L: 30846 D: 79140
http://tests.stockfishchess.org/tests/view/5cabbdb20ebc5925cf00b86c
LTC:
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 30708 W: 5296 L: 5043 D: 20369
http://tests.stockfishchess.org/tests/view/5cabff760ebc5925cf00c22d
Bench: 3445945
Adding a clamp function makes some of these range limitations a bit prettier and removes some #include's.
STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 28117 W: 6300 L: 6191 D: 15626
http://tests.stockfishchess.org/tests/view/5c9aa1df0ebc5925cfff8fcc
Non functional change.
This is a functional simplification of the Outposts array
moving it to a single value. This is a duplicate PR because
I couldn't figure out how to fix the original one.
The idea is from @31m059 with formatting recommendations by @snicolet.
See #1940 for additional information.
STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 23933 W: 5279 L: 5162 D: 13492
http://tests.stockfishchess.org/tests/view/5c3575800ebc596a450c5ecb
LTC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 41718 W: 6919 L: 6831 D: 27968
http://tests.stockfishchess.org/tests/view/5c358c440ebc596a450c6117
bench 3783543
There was a simplification attempt last week for the tropism
term in king danger, which passed STC but failed LTC. This
was an indirect sign that maybe the tropism factor was sightly
untuned in current master, so we tried to change it from 1/4
to 5/16.
STC:
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 28098 W: 6264 L: 5990 D: 15844
http://tests.stockfishchess.org/tests/view/5c518db60ebc593af5d4e306
LTC:
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 103709 W: 17387 L: 16923 D: 69399
http://tests.stockfishchess.org/tests/view/5c52a5510ebc592fc7baea8b
Bench: 4016000
Remove overlapping safe checks from kingdanger:
- rook and queen checks from the same square: rook check is preferred
- bishop and queen checks form the same square: queen check is preferred
Increase bishop and rook check values as a compensation.
STC
LLR: 2.95 (-2.94,2.94) [0.50,4.50]
Total: 27480 W: 6111 L: 5813 D: 15556
http://tests.stockfishchess.org/tests/view/5c521d050ebc593af5d4e66a
LTC
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 78500 W: 13145 L: 12752 D: 52603
http://tests.stockfishchess.org/tests/view/5c52b9460ebc592fc7baecc5
Closes https://github.com/official-stockfish/Stockfish/pull/1983
------------------------------------------
I have quite a few ideas of how to improve this patch.
- actually rethinking it now it will maybe be useful to discount
queen/bishop checks if there is only one square that they can
give check from and it's "occupied" by more valuable check. Right
now count of this squares does not really matter.
- maybe some small extra bonus can be given for overlapping checks.
- some ideas about using popcount() on safechecks can be retried.
- tune this safecheck values since they were more or less randomly handcrafted in this patch.
Bench: 3216489
Small changes in initiative(). For Pawn PSQT, endgame values for d6-e6 and d7-e7 are now symmetric. The MG value of d2 is now smaller than e2 (d2=13, e2=21 now compared to d2=19, e2=16 before). The MG values of h5-h6-h7 also increased so this might encourage stockfish for more h-pawn pushes.
STC
LLR: -2.96 (-2.94,2.94) [0.00,4.00]
Total: 81141 W: 17933 L: 17777 D: 45431
http://tests.stockfishchess.org/tests/view/5c4017350ebc5902bb5cf237
LTC
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 83078 W: 13883 L: 13466 D: 55729
http://tests.stockfishchess.org/tests/view/5c40763f0ebc5902bb5cff09
Bench: 3266398
A single popcount in evaluate.cpp replaces all openFiles stuff in pawns. It doesn't seem to affect performance at all.
STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 28103 W: 6134 L: 6025 D: 15944
http://tests.stockfishchess.org/tests/view/5b7d70a20ebc5902bdbb1999
No functional change.
Recent tests by @xoto10, @Vizvezdenec, and myself seemed to hint that Elo could
be gained by expanding the number of cases where king safety is applied. Several
users (@Spliffjiffer, @Vizvezdenec) have anticipated benefits specifically in
evaluation of tactics. It appears that we actually do not need to restrict the
cases in which we initialize and evaluate king safety at all: initializing and
evaluating it in every position appears roughly Elo-neutral at STC and possibly
a substantial Elo gain at LTC.
Any explanation for this scaling is, at this point, conjecture. Assuming it is
not due to chance, my hypothesis is that initialization of king safety in all
positions is a mild slowdown, offset by an Elo gain of evaluating king safety
in all positions. At STC this produces Elo gains and losses that offset each
other, while at longer time control the slowdown is much less important, leaving
only the Elo gain. It probably helps SF to explore king attacks much earlier in
search with high numbers of enemy pieces concentrating but not essentially attacking
king ring.
Thanks to @xoto10 and @Vizvezdenec for helping run my LTC!
Closes https://github.com/official-stockfish/Stockfish/pull/1906
STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 35432 W: 7815 L: 7721 D: 19896
http://tests.stockfishchess.org/tests/view/5c24779d0ebc5902ba131b26
LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 12887 W: 2217 L: 2084 D: 8586
http://tests.stockfishchess.org/tests/view/5c25049a0ebc5902ba132586
Bench: 3163951
------------------
How to continue from there?
* Next step will be to tune all the king danger terms once more after that :-)
~stronglyProtected is quite similar to ~attackedBy[Them][PAWN] & ~attackedBy2[Them],
the only difference appears to be that the former includes squares attacked twice
by both sides. The resulting logic is simpler, and the change appears to be at least
Elo-neutral at both STC and LTC.
STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 35924 W: 7978 L: 7885 D: 20061
http://tests.stockfishchess.org/tests/view/5c14a5c00ebc5902ba11ed72
LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 37078 W: 6125 L: 6030 D: 24923
http://tests.stockfishchess.org/tests/view/5c14ae880ebc5902ba11eed8
Bench: 3646542
I've gone through the RENAME/REFORMATTING thread and changed everything I could find, plus a few more. With this, let's close the previous issue and open another.
No functional change.
Exclude doubly protected by pawns squares when calculating attackers on
king ring. Idea of this patch is not to count attackers if they attack
only squares that are protected by two pawns.
STC
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 70040 W: 15476 L: 15002 D: 39562
http://tests.stockfishchess.org/tests/view/5c0354860ebc5902bcee1106
LTC
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 16530 W: 2795 L: 2607 D: 11128
http://tests.stockfishchess.org/tests/view/5c0385080ebc5902bcee14b5
This is third king safety patch in recent times so we probably need
retuning of king safety parameters.
Bench: 3057978
Tropism in kingdanger was simplified away in this pull request #1821.
This patch reintroduces tropism in kingdanger with using quadratic scaling.
Passed STC http://tests.stockfishchess.org/tests/view/5bf7c1b10ebc5902bced1f8f
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 52803 W: 11835 L: 11442 D: 29526
Passed LTC http://tests.stockfishchess.org/tests/view/5bf816e90ebc5902bced24f1
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 17204 W: 2988 L: 2795 D: 11421
How do we continue from there?
I've recently tried to introduce tropism difference term in kingdanger which
passed STC 6 times but failed LTC all the time. Maybe using quadratic scaling
for it will also be helpful.
Bench 4041387
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
STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 51883 W: 11297 L: 10915 D: 29671
http://tests.stockfishchess.org/tests/view/5bf1e2ee0ebc595e0ae3cacd
LTC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 15859 W: 2752 L: 2565 D: 10542
http://tests.stockfishchess.org/tests/view/5bf337980ebc5902bcecbf62
Notes:
(1) The bonus value has not been carefully tested, so it may be possible
to find slightly better values.
(2) Plan is to now try adding similar restriction for pawns. I wanted to
include that as part of this pull request, but I was advised to do it as
two separate pull requests. STC is currently running here, but may not add
enough value to pass green.
Bench: 3679086
Preparation commit for the upcoming Stockfish 10 version, giving a chance to catch last minute feature bugs and evaluation regression during the one-week code freeze period. Also changing the copyright dates to include 2019.
No functional change
STC:
LLR: -2.96 (-2.94,2.94) [0.00,4.00]
Total: 84697 W: 18173 L: 18009 D: 48515
http://tests.stockfishchess.org/tests/view/5bea366f0ebc595e0ae34793
LTC:
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 157625 W: 25533 L: 24893 D: 107199
http://tests.stockfishchess.org/tests/view/5be8b69e0ebc595e0ae33024
Personally, I feel like SF has been tuned to death recently and that we
need to step away from existing-parameter tunes for a bit and focus more
on new ideas. I don't really think there's much more ELO in these tunes
(for now). For me at least, this was the last existing-parameter tune I'll
be running for quite a while. Cheers!
Bench: 3572567
It does not appear to be not necessary or advantageous to
conditionally initialize kingRing[Us] or kingAttackersCount[Them],
so the 'else' can be removed.
STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 22873 W: 4923 L: 4804 D: 13146
http://tests.stockfishchess.org/tests/view/5be9a8270ebc595e0ae33c7e
No functional change
We don't need to pass the king square as an explicit parameter to the functions
king_safety() and do_king_safety() since we already pass in the position.
STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 69686 W: 14894 L: 14866 D: 39926
http://tests.stockfishchess.org/tests/view/5be84ac20ebc595e0ae3283c
No functional change.
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
