This patch updates the stat_bonus() function (used in the history tables to
help move ordering), keeping the same quadratic for small depths but changing
the values for depth >= 9:
The old bonus formula was increasing from zero at depth 1 to 4100 at depth 14,
then used the strange, small value of 73 for all depths >= 15.
The new bonus formula increases from 0 at depth 1 to 2000 at depth 8, then
keeps 2000 for all depths >= 8.
passed STC:
LLR: 2.94 (-2.94,2.94) <-0.50,2.50>
Total: 169624 W: 42875 L: 42454 D: 84295
Ptnml(0-2): 585, 19340, 44557, 19729, 601
https://tests.stockfishchess.org/tests/view/615bd69e9d256038a969b97c
passed LTC:
LLR: 3.07 (-2.94,2.94) <0.50,3.50>
Total: 37336 W: 9456 L: 9191 D: 18689
Ptnml(0-2): 20, 3810, 10747, 4067, 24
https://tests.stockfishchess.org/tests/view/615c75d99d256038a969b9b2
closes https://github.com/official-stockfish/Stockfish/pull/3731
Bench: 6261865
In master, during singular move analysis, when both the transposition value
and a reduced search for the other moves seem to indicate a fail high, we
heuristically prune the whole subtree and return an fail high score.
This patch is a little bit more cautious in this case, and instead of the
risky cutoff, we now search the ttMove with a reduced depth (by two plies).
STC:
https://tests.stockfishchess.org/tests/view/614dafe07bdc23e77ceb8a89
LLR: 2.94 (-2.94,2.94) <-0.50,2.50>
Total: 46728 W: 11909 L: 11666 D: 23153
Ptnml(0-2): 181, 5288, 12168, 5561, 166
LTC:
https://tests.stockfishchess.org/tests/view/614dc84abe4c07e0ecac3c95
LLR: 2.94 (-2.94,2.94) <0.50,3.50>
Total: 74520 W: 18809 L: 18450 D: 37261
Ptnml(0-2): 45, 7735, 21346, 8084, 50
closes https://github.com/official-stockfish/Stockfish/pull/3718
Bench: 5499262
This patch relax a little bit the condition for doubly singular moves
(ie moves that are so forced that we think that they deserve a local
double extension of the search). We lower the margin and allow up to
six such double extensions in the path between the root and the critical
node.
Original idea by Siad Daboul (@TopoIogist) in PR #3709
Tested with the previous commit:
passed STC:
LLR: 2.94 (-2.94,2.94) <-0.50,2.50>
Total: 33048 W: 8458 L: 8236 D: 16354
Ptnml(0-2): 120, 3701, 8660, 3923, 120
https://tests.stockfishchess.org/tests/view/614b24347bdc23e77ceb88fe
passed LTC:
LLR: 2.95 (-2.94,2.94) <0.50,3.50>
Total: 54176 W: 13712 L: 13406 D: 27058
Ptnml(0-2): 36, 5653, 15399, 5969, 31
https://tests.stockfishchess.org/tests/view/614b3b727bdc23e77ceb8911
closes https://github.com/official-stockfish/Stockfish/pull/3714
Bench: 5792377
This patch detects some search explosions (due to double extensions in
search.cpp) which can happen in some pathological positions, and takes
measures to ensure progress in search even for these pathological situations.
While a small number of double extensions can be useful during search
(for example to resolve a tactical sequence), a sustained regime of
double extensions leads to search explosion and a non-finishing search.
See the discussion in https://github.com/official-stockfish/Stockfish/pull/3544
and the issue https://github.com/official-stockfish/Stockfish/issues/3532 .
The implemented algorithm is the following:
a) at each node during search, store the current depth in the stack.
Double extensions are by definition levels of the stack where the
depth at ply N is strictly higher than depth at ply N-1.
b) during search, calculate for each thread a running average of the
number of double extensions in the last 4096 visited nodes.
c) if one thread has more than 2% of double extensions for a sustained
period of time (6 millions consecutive nodes, or about 4 seconds on
my iMac), we decide that this thread is in an explosion state and
we calm down this thread by preventing it to do any double extension
for the next 6 millions nodes.
To calculate the running averages, we also introduced a auxiliary class
generalizing the computations of ttHitAverage variable we already had in
code. The implementation uses an exponential moving average of period 4096
and resolution 1/1024, and all computations are done with integers for
efficiency.
-----------
Example where the patch solves a search explosion:
```
./stockfish
ucinewgame
position fen 8/Pk6/8/1p6/8/P1K5/8/6B1 w - - 37 130
go infinite
```
This algorithm does not affect search in normal, non-pathological positions.
We verified, for instance, that the usual bench is unchanged up to depth 20
at least, and that the node numbers are unchanged for a search of the starting
position at depth 32.
-------------
See https://github.com/official-stockfish/Stockfish/pull/3714
Bench: 5575265
In the so-called "hybrid" method of evaluation of current master, we use the
classical eval (because of its speed) instead of the NNUE eval when the classical
material balance approximation hints that the position is "winning enough" to
rely on the classical eval.
This trade-off idea between speed and accuracy works well in general, but in
some fortress positions the classical eval is just bad. So in shuffling branches
of the search tree, we (slowly) increase the thresehold so that eventually we
don't trust classical anymore and switch to NNUE evaluation.
This patch increases that threshold faster, so that we switch to NNUE quicker
in shuffling branches. Idea is to incite Stockfish to spend less time in fortresses
lines in the search tree, and spend more time searching the critical lines.
passed STC:
LLR: 2.96 (-2.94,2.94) <-0.50,2.50>
Total: 47872 W: 3908 L: 3720 D: 40244
Ptnml(0-2): 122, 3053, 17419, 3199, 143
https://tests.stockfishchess.org/tests/view/60cef34b457376eb8bcab79d
passed LTC:
LLR: 2.93 (-2.94,2.94) <0.50,3.50>
Total: 73616 W: 2326 L: 2143 D: 69147
Ptnml(0-2): 21, 1940, 32705, 2119, 23
https://tests.stockfishchess.org/tests/view/60cf6d842114332881e73528
Retested at LTC against lastest master:
LLR: 2.93 (-2.94,2.94) <0.50,3.50>
Total: 18264 W: 642 L: 532 D: 17090
Ptnml(0-2): 6, 479, 8055, 583, 9
https://tests.stockfishchess.org/tests/view/60d18cd540925195e7a6c351
closes https://github.com/official-stockfish/Stockfish/pull/3578
Bench: 5139233
This patch removes the UCI option for setting Contempt in classical evaluation.
It is exactly equivalent to using Contempt=0 for the UCI contempt value and keeping
the dynamic part in the algo (renaming this dynamic part `trend` to better describe
what it does). We have tried quite hard to implement a working Contempt feature for
NNUE but nothing really worked, so it is probably time to give up.
Interested chess fans wishing to keep playing with the UCI option for Contempt and
use it with the classical eval are urged to download the version tagged "SF_Classical"
of Stockfish (dated 31 July 2020), as it was the last version where our search
algorithm was tuned for the classical eval and is probably our strongest classical
player ever: https://github.com/official-stockfish/Stockfish/tags
Passed STC:
LLR: 2.95 (-2.94,2.94) <-2.50,0.50>
Total: 72904 W: 6228 L: 6175 D: 60501
Ptnml(0-2): 221, 5006, 25971, 5007, 247
https://tests.stockfishchess.org/tests/view/60c98bf9457376eb8bcab18d
Passed LTC:
LLR: 2.93 (-2.94,2.94) <-2.50,0.50>
Total: 45168 W: 1601 L: 1547 D: 42020
Ptnml(0-2): 38, 1331, 19786, 1397, 32
https://tests.stockfishchess.org/tests/view/60c9c7fa457376eb8bcab1bb
closes https://github.com/official-stockfish/Stockfish/pull/3575
Bench: 4947716
This patch increase the weight of pawns and pieces from 28 to 32
in the scaling formula we apply to the output of the NNUE pure eval.
Increasing this gradient for pawns and pieces means that Stockfish
will try a little harder to keep material when she has the advantage,
and try a little bit harder to escape into an endgame when she is
under pressure.
STC:
LLR: 2.93 (-2.94,2.94) <-0.50,2.50>
Total: 53168 W: 4371 L: 4177 D: 44620
Ptnml(0-2): 160, 3389, 19283, 3601, 151
https://tests.stockfishchess.org/tests/view/60cefd1d457376eb8bcab7ab
LTC:
LLR: 2.94 (-2.94,2.94) <0.50,3.50>
Total: 10888 W: 386 L: 288 D: 10214
Ptnml(0-2): 3, 260, 4821, 356, 4
https://tests.stockfishchess.org/tests/view/60cf709d2114332881e7352b
closes https://github.com/official-stockfish/Stockfish/pull/3571
Bench: 4965430
This reverts commit "Fix for Cygwin's environment build-profile", as it was
giving errors for "make clean" on some Windows environments. See comments in
https://github.com/official-stockfish/Stockfish/commit/68bf362ea2385a641be9f5ed9ce2acdf55a1ecf1
Possibly somebody can propose a solution that would fix Cygwin builds and
not break on other system too, stay tuned! :-)
No functional change
Cleaner vector code structure in feature transformer. This patch just
regroups the parts of the inner loop for each SIMD instruction set.
Tested for non-regression:
LLR: 2.96 (-2.94,2.94) <-2.50,0.50>
Total: 115760 W: 9835 L: 9831 D: 96094
Ptnml(0-2): 326, 7776, 41715, 7694, 369
https://tests.stockfishchess.org/tests/view/60b96b39457376eb8bcaa26e
It would be nice if a future patch could use some of the macros at
the top of the file to unify the code between the distincts SIMD
instruction sets (of course, unifying the Relu will be the challenge).
closes https://github.com/official-stockfish/Stockfish/pull/3506
No functional change
This simplification patch implements two changes:
1. it simplifies away the so-called "lazy" path in the NNUE evaluation internals,
where we trusted the psqt head alone to avoid the costly "positional" head in
some cases;
2. it raises a little bit the NNUEThreshold1 in evaluate.cpp (from 682 to 800),
which increases the limit where we switched from NNUE eval to Classical eval.
Both effects increase the number of positional evaluations done by our new net
architecture, but the results of our tests below seem to indicate that the loss
of speed will be compensated by the gain of eval quality.
STC:
LLR: 2.95 (-2.94,2.94) <-2.50,0.50>
Total: 26280 W: 2244 L: 2137 D: 21899
Ptnml(0-2): 72, 1755, 9405, 1810, 98
https://tests.stockfishchess.org/tests/view/60ae73f112066fd299795a51
LTC:
LLR: 2.95 (-2.94,2.94) <-2.50,0.50>
Total: 20592 W: 750 L: 677 D: 19165
Ptnml(0-2): 9, 614, 8980, 681, 12
https://tests.stockfishchess.org/tests/view/60ae88e812066fd299795a82
closes https://github.com/official-stockfish/Stockfish/pull/3503
Bench: 3817907
Our new nets output two values for the side to move in the last layer.
We can interpret the first value as a material evaluation of the
position, and the second one as the dynamic, positional value of the
location of pieces.
This patch changes the balance for the (materialist, positional) parts
of the score from (128, 128) to (121, 135) when the piece material is
equal between the two players, but keeps the standard (128, 128) balance
when one player is at least an exchange up.
Passed STC:
LLR: 2.93 (-2.94,2.94) <-0.50,2.50>
Total: 15936 W: 1421 L: 1266 D: 13249
Ptnml(0-2): 37, 1037, 5694, 1134, 66
https://tests.stockfishchess.org/tests/view/60a82df9ce8ea25a3ef0408f
Passed LTC:
LLR: 2.94 (-2.94,2.94) <0.50,3.50>
Total: 13904 W: 516 L: 410 D: 12978
Ptnml(0-2): 4, 374, 6088, 484, 2
https://tests.stockfishchess.org/tests/view/60a8bbf9ce8ea25a3ef04101
closes https://github.com/official-stockfish/Stockfish/pull/3492
Bench: 3856635
The Tempo variable was introduced 10 years ago in our search because the
classical evaluation function was antisymmetrical in White and Black by design
to gain speed:
Eval(White to play) = -Eval(Black to play)
Nowadays our neural networks know which side is to play in a position when
they evaluate a position and are trained on real games, so the neural network
encodes the advantage of moving as an output of search. This patch shows that
the Tempo variable is not necessary anymore.
STC:
LLR: 2.94 (-2.94,2.94) <-2.50,0.50>
Total: 33512 W: 2805 L: 2709 D: 27998
Ptnml(0-2): 80, 2209, 12095, 2279, 93
https://tests.stockfishchess.org/tests/view/60a44ceace8ea25a3ef03d30
LTC:
LLR: 2.95 (-2.94,2.94) <-2.50,0.50>
Total: 53920 W: 1807 L: 1760 D: 50353
Ptnml(0-2): 16, 1617, 23650, 1658, 19
https://tests.stockfishchess.org/tests/view/60a477f0ce8ea25a3ef03d49
We also tried a match (20000 games) at STC using purely classical, result was neutral:
https://tests.stockfishchess.org/tests/view/60a4eebcce8ea25a3ef03db5
Note: there are two locations left in search.cpp where we assume antisymmetry
of evaluation (in relation with a speed optimization for null moves in lines
770 and 1439), but as the values are just used for heuristic pruning this
approximation should not hurt too much because the order of magnitude is still
true most of the time.
closes https://github.com/official-stockfish/Stockfish/pull/3481
Bench: 4015864
- Comment for Countemove pruning -> Continuation history
- Fix comment in input_slice.h
- Shorter lines in Makefile
- Comment for scale factor
- Fix comment for pinners in see_ge()
- Change Thread.id() signature to size_t
- Trailing space in reprosearch.sh
- Add Douglas Matos Gomes to the AUTHORS file
- Introduce comment for undo_null_move()
- Use Stockfish coding style for export_net()
- Change date in AUTHORS file
closes https://github.com/official-stockfish/Stockfish/pull/3416
No functional change
We introduce a metric for each internal node in search, called DistanceFromPV.
This distance indicated how far the current node is from the principal variation.
We then use this distance to search the nodes which are close to the PV a little
deeper (up to 4 plies deeper than the PV): this improves the quality of the search
at these nodes and bring better updates for the PV during search.
STC:
LLR: 2.96 (-2.94,2.94) {-0.25,1.25}
Total: 54936 W: 5047 L: 4850 D: 45039
Ptnml(0-2): 183, 3907, 19075, 4136, 167
https://tests.stockfishchess.org/tests/view/6037b88e7f517a561bc4a392
LTC:
LLR: 2.95 (-2.94,2.94) {0.25,1.25}
Total: 49608 W: 1880 L: 1703 D: 46025
Ptnml(0-2): 22, 1514, 21555, 1691, 22
https://tests.stockfishchess.org/tests/view/6038271b7f517a561bc4a3cb
Closes https://github.com/official-stockfish/Stockfish/pull/3369
Bench: 5037279
• reorder some sections of the README file
• add reference to the AUTHORS file
• rename Syzygybases to Syzygy tablebases
• add pointer to the Discord channel
• more precise info about the GPLv3 licence
No functional change
This patch give a small bonus to incite the attacking side to keep more
pawns on the board.
A consequence of this bonus is that Stockfish will tend to play positions
slightly more closed on average than master, especially when it believes
that it has an advantage.
To lower the risk of blockades where Stockfish start shuffling without
progress, we also implement a progressive decrease of the evaluation
value with the 50 moves counter (along with the necessary aging of the
transposition table to reduce the impact of the Graph History Interaction
problem): since the evaluation decreases during shuffling phases, the
engine will tend to examine the consequences of pawn breaks faster during
the search.
Passed STC:
LLR: 2.96 (-2.94,2.94) {-0.25,1.25}
Total: 26184 W: 2406 L: 2252 D: 21526
Ptnml(0-2): 85, 1784, 9223, 1892, 108
https://tests.stockfishchess.org/tests/view/600cc08b735dd7f0f0352c06
Passed LCT:
LLR: 2.95 (-2.94,2.94) {0.25,1.25}
Total: 199768 W: 7695 L: 7191 D: 184882
Ptnml(0-2): 85, 6478, 86269, 6952, 100
https://tests.stockfishchess.org/tests/view/600ccd28735dd7f0f0352c10
Closes https://github.com/official-stockfish/Stockfish/pull/3321
Bench: 3988915
We now include the total pawn count in the scaling factor for the output
of the NNUE evaluation network. This should have the effect of trying to
keep more pawns when SF has the advantage, but exchange them when she
is defending.
Thanks to Alexander Pagel (Lolligerhans) for the idea of using the
value of pawns to ease the comparison with the rest of the material
estimation.
Passed STC:
LLR: 2.93 (-2.94,2.94) {-0.25,1.25}
Total: 15072 W: 1700 L: 1539 D: 11833
Ptnml(0-2): 65, 1202, 4845, 1355, 69
https://tests.stockfishchess.org/tests/view/5f7235a63b22d6afa50699b3
Passed LTC:
LLR: 2.93 (-2.94,2.94) {0.25,1.25}
Total: 25880 W: 1270 L: 1124 D: 23486
Ptnml(0-2): 23, 980, 10788, 1126, 23
https://tests.stockfishchess.org/tests/view/5f723b483b22d6afa5069a99
closes https://github.com/official-stockfish/Stockfish/pull/3164
Bench: 3776081
Current master uses a constant scale factor of 5/4 = 1.25 for the output
of the NNUE network, for compatibility with search and classical evaluation.
We modify this scale factor to make it dependent on the phase of the game,
going from about 1.5 in the opening to 1.0 for pure pawn endgames.
This helps Stockfish to avoid exchanges of pieces (heavy pieces in particular)
when she has the advantage, keeping more material on the board when attacking.
Passed STC:
LLR: 2.95 (-2.94,2.94) {-0.25,1.25}
Total: 14744 W: 1771 L: 1599 D: 11374
Ptnml(0-2): 87, 1184, 4664, 1344, 93
https://tests.stockfishchess.org/tests/view/5f6fb0a63b22d6afa506904f
Passed LTC:
LLR: 2.95 (-2.94,2.94) {0.25,1.25}
Total: 8912 W: 512 L: 393 D: 8007
Ptnml(0-2): 7, 344, 3637, 459, 9
https://tests.stockfishchess.org/tests/view/5f6fcf533b22d6afa5069066
closes https://github.com/official-stockfish/Stockfish/pull/3154
Bench: 3943952
- Clean signature of functions in namespace NNUE
- Add comment for countermove based pruning
- Remove bestMoveCount variable
- Add const qualifier to kpp_board_index array
- Fix spaces in get_best_thread()
- Fix indention in capture LMR code in search.cpp
- Rename TtmemDeleter to LargePageDeleter
Closes https://github.com/official-stockfish/Stockfish/pull/3063
No functional change
covers the most important cases from the user perspective:
It embeds the default net in the binary, so a download of that binary will result
in a working engine with the default net. The engine will be functional in the default mode
without any additional user action.
It allows non-default nets to be used, which will be looked for in up to
three directories (working directory, location of the binary, and optionally a specific default directory).
This mechanism is also kept for those developers that use MSVC,
the one compiler that doesn't have an easy mechanism for embedding data.
It is possible to disable embedding, and instead specify a specific directory, e.g. linux distros might want to use
CXXFLAGS="-DNNUE_EMBEDDING_OFF -DDEFAULT_NNUE_DIRECTORY=/usr/share/games/stockfish/" make -j ARCH=x86-64 profile-build
passed STC non-regression:
https://tests.stockfishchess.org/tests/view/5f4a581c150f0aef5f8ae03a
LLR: 2.95 (-2.94,2.94) {-1.25,-0.25}
Total: 66928 W: 7202 L: 7147 D: 52579
Ptnml(0-2): 291, 5309, 22211, 5360, 293
closes https://github.com/official-stockfish/Stockfish/pull/3070
fixes https://github.com/official-stockfish/Stockfish/issues/3030
No functional change.
Do not show the details of the default architecture for a simple "make help"
invocation, as the details are most likely to confuse beginners. Instead we
make it clear which architecture is the default and put an example at the end
of the Makefile as an incentative to use "make help ARCH=blah" to discover
the flags used by the different architectures.
```
make help
make help ARCH=x86-64-ssse3
```
Also clean-up and modernize a bit the Makefile examples while at it.
closes https://github.com/official-stockfish/Stockfish/pull/2996
No functional change
We lower the endgame value of the evaluation when we detect that there
is only one queen left on the board (more precisely, we use a scale
factor of 37/64, or about 0.58, for the endgame part of the evaluation).
Hopefully this helps a little bit for the assessment of positions with
queen imbalance, which are one of the well-known Stockfish weaknesses.
STC:
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 21600 W: 4176 L: 3955 D: 13469
Ptnml(0-2): 351, 2457, 5003, 2598, 391
https://tests.stockfishchess.org/tests/view/5ef871b6020eec13834a94e8
LTC:
LLR: 2.97 (-2.94,2.94) {0.25,1.75}
Total: 248328 W: 30596 L: 29720 D: 188012
Ptnml(0-2): 1544, 22345, 75665, 22911, 1699
https://tests.stockfishchess.org/tests/view/5ef87aec020eec13834a94fe
Closes https://github.com/official-stockfish/Stockfish/pull/2781
Bench: 4441323
We increase a little bit the midgame value of pawns on a4, h4, a6 and h6.
Original idea by Malcolm Campbell, who tried the version restricted to the
pawns on the H column a couple of weeks ago and got a patch which almost
passed LTC. The current pull request just adds the same idea for pawns on
the A column.
Possible follow-ups: maybe tweak the a5/h5 pawn values, and/or add a malus
for very low king mobility in midgame?
STC:
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 33416 W: 6516 L: 6275 D: 20625
Ptnml(0-2): 575, 3847, 7659, 4016, 611
https://tests.stockfishchess.org/tests/view/5ee6c4e687586124bc2c10d4
LTC:
LLR: 2.95 (-2.94,2.94) {0.25,1.75}
Total: 134368 W: 16869 L: 16319 D: 101180
Ptnml(0-2): 908, 12083, 40708, 12521, 964
https://tests.stockfishchess.org/tests/view/5ee74e60aae8aec816ab756a
closes https://github.com/official-stockfish/Stockfish/pull/2747
Bench: 5299456
We replace the current decrease of the complexity term in initiative
when shuffling by a direct damping of the evaluation. This scheme may
have two benefits over the initiative approach:
a) the damping effect is more brutal for fortresses with heavy pieces
on the board, because the initiative term is almost an endgame term;
b) the initiative implementation had a funny side effect, almost a bug,
in the rare positions where mg > 0, eg < 0 and the tampered eval
returned a positive value (ie with heavy pieces still on the board):
sending eg to zero via shuffling would **increase** the tampered
eval instead of decreasing it, which is somewhat illogical. This
patch avoids this phenomenon.
STC:
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 43072 W: 8373 L: 8121 D: 26578
Ptnml(0-2): 729, 4954, 9940, 5162, 751
https://tests.stockfishchess.org/tests/view/5ee008ebf29b40b0fc95ade2
LTC:
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 37376 W: 4816 L: 4543 D: 28017
Ptnml(0-2): 259, 3329, 11286, 3508, 306
https://tests.stockfishchess.org/tests/view/5ee03b06f29b40b0fc95ae0c
Closes https://github.com/official-stockfish/Stockfish/pull/2727
Bench: 4757174
This patch is a combinaison of two recent parameters tweaks which had
failed narrowly (yellow) at long time control:
• improvement in move ordering during search by softening the distinction
between bad captures and good captures during move generation, leading
to improved awareness of Stockfish of potential piece sacrifices (idea
by Rahul Dsilva)
• increase in the weight of pawns in the "initiative" part of the evaluation
function. With this change Stockfish should have more incentive to exchange
pawns when losing, and to keep pawns when winning.
STC:
LLR: 2.93 (-2.94,2.94) {-0.50,1.50}
Total: 10704 W: 2178 L: 1974 D: 6552
Ptnml(0-2): 168, 1185, 2464, 1345, 190
https://tests.stockfishchess.org/tests/view/5ec5553b377121ac09e1023d
LTC:
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 60592 W: 7835 L: 7494 D: 45263
Ptnml(0-2): 430, 5514, 18086, 5817, 449
https://tests.stockfishchess.org/tests/view/5ec55ca2377121ac09e10249
Closes https://github.com/official-stockfish/Stockfish/pull/2691
Bench: 4519117
simplify the usage of the 50 moves counter,
moving it frome the scale factor to initiative.
This patch was inspired by recent games where a blocked or semi-blocked position
was 'blundered', by moving a pawn, into a lost endgame. This patch improves this situation,
finding a more robust move more often.
for example (1s searches with many threads):
```
FEN 8/p3kp2/Pp2p3/1n2PpP1/5P2/1Kp5/8/R7 b - - 68 143
master:
6 bestmove b5c7
6 bestmove e7e8
12 bestmove e7d8
176 bestmove e7d7
patch:
3 bestmove b5c7
5 bestmove e7d8
192 bestmove e7d7
```
fixes https://github.com/official-stockfish/Stockfish/issues/2620
the patch also tests well
passed STC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 50168 W: 9508 L: 9392 D: 31268
Ptnml(0-2): 818, 5873, 11616, 5929, 848
https://tests.stockfishchess.org/tests/view/5ebb07287dd5693aad4e680b
passed LTC
LLR: 2.93 (-2.94,2.94) {-1.50,0.50}
Total: 7520 W: 981 L: 870 D: 5669
Ptnml(0-2): 49, 647, 2256, 760, 48
https://tests.stockfishchess.org/tests/view/5ebbff747dd5693aad4e6858
closes https://github.com/official-stockfish/Stockfish/pull/2666
Bench: 4395562
Official release version of Stockfish 11.
Bench: 5156767
-----------------------
It is our pleasure to release Stockfish 11 to our fans and supporters.
Downloads are freely available at http://stockfishchess.org/download/
This version 11 of Stockfish is 50 Elo stronger than the last version, and
150 Elo stronger than the version which famously lost a match to AlphaZero
two years ago. This makes Stockfish the strongest chess engine running on
your smartphone or normal desktop PC, and we estimate that on a modern four
cores CPU, Stockfish 11 could give 1:1000 time odds to the human chess champion
having classical time control, and be on par with him. More specific data,
including nice cumulative curves for the progression of Stockfish strength
over the last seven years, can be found on [our progression page][1], at
[Stefan Pohl site][2] or at [NextChessMove][3].
In October 2019 Stockfish has regained its crown in the TCEC competition,
beating in the superfinal of season 16 an evolution of the neural-network
engine Leela that had won the previous season. This clash of style between an
alpha-beta and an neural-network engine produced spectacular chess as always,
with Stockfish [emerging victorious this time][0].
Compared to Stockfish 10, we have made hundreds of improvements to the
[codebase][4], from the evaluation function (improvements in king attacks,
middlegame/endgame transitions, and many more) to the search algorithm (some
innovative coordination methods for the searching threads, better pruning of
unsound tactical lines, etc), and fixed a couple of bugs en passant.
Our testing framework [Fishtest][5] has also seen its share of improvements
to continue propelling Stockfish forward. Along with a lot of small enhancements,
Fishtest has switched to new SPRT bounds to increase the chance of catching Elo
gainers, along with a new testing book and the use of pentanomial statistics to
be more resource-efficient.
Overall the Stockfish project is an example of open-source at its best, as
its buzzing community of programmers sharing ideas and daily reviewing their
colleagues' patches proves to be an ideal form to develop innovative ideas for
chess programming, while the mathematical accuracy of the testing framework
allows us an unparalleled level of quality control for each patch we put in
the engine. If you wish, you too can help our ongoing efforts to keep improving
it, just [get involved][6] :-)
Stockfish is also special in that every chess fan, even if not a programmer,
[can easily help][7] the team to improve the engine by connecting their PC to
Fishtest and let it play some games in the background to test new patches.
Individual contributions vary from 1 to 32 cores, but this year Bojun Guo
made it a little bit special by plugging a whole data center during the whole
year: it was a vertiginous experience to see Fishtest spikes with 17466 cores
connected playing [25600 games/minute][8]. Thanks Guo!
The Stockfish team
[0]: <http://mytcecexperience.blogspot.com/2019/10/season-16-superfinal-games-91-100.html>
[1]: <https://github.com/glinscott/fishtest/wiki/Regression-Tests>
[2]: <https://www.sp-cc.de/index.htm>
[3]: <https://nextchessmove.com/dev-builds>
[4]: <https://github.com/official-stockfish/Stockfish>
[5]: <https://tests.stockfishchess.org/tests>
[6]: <https://stockfishchess.org/get-involved/>
[7]: <https://github.com/glinscott/fishtest/wiki>
[8]: <https://groups.google.com/forum/?fromgroups=#!topic/fishcooking/lebEmG5vgng%5B1-25%5D>
This patch shows a description of the compiler used to compile Stockfish,
when starting from the console.
Usage:
```
./stockfish
compiler
```
Example of output:
```
Stockfish 120120 64 POPCNT by T. Romstad, M. Costalba, J. Kiiski, G. Linscott
Compiled by clang++ 9.0.0 on Apple
__VERSION__ macro expands to: 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.38)
```
No functional change
This reverts the previous commit. The PSQT changes in this previous
commit originated from tests against quite an old version of master
which did not include the other PSQT changes of 474d133 for the other
pieces, and there might be some unknown interactions between the PSQT
tables. So we made a non-regression test of the last commit against the
last-but-one commit. This test failed, leading to the revert decision.
Failed non-regression test:
LLR: -2.96 (-2.94,2.94) [-3.00,1.00]
Total: 95536 W: 15047 L: 15347 D: 65142
http://tests.stockfishchess.org/tests/view/5dc0ba1d0ebc5904493b0112
Closes https://github.com/official-stockfish/Stockfish/pull/2395
Bench: 4362323
- Cleanups by Alain
- Group king attacks and king defenses
- Signature of futility_move_count()
- Use is_discovery_check_on_king()
- Simplify backward definition
- Use static asserts in move generator
- Factor a statement in move generator
No functional change
Revert the previous patch now that the binary for the super-final
of TCEC season 16 has been sent.
Maybe the feature of showing the name of compiler will be added to the
master branch in the future. But we may use a cleaner way to code it, see
some ideas using the Makefile approach at the end of pull request #2327 :
https://github.com/official-stockfish/Stockfish/pull/2327
Bench: 3618154
This patch shows a description of the compiler used to compile Stockfish,
when starting from the console.
Usage:
```
./stockfish
compiler
```
Example of output:
```
Stockfish 240919 64 POPCNT by T. Romstad, M. Costalba, J. Kiiski, G. Linscott
Compiled by clang++ 9.0.0 on Apple
__VERSION__ macro expands to: 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.38)
```
No functional change
Author: @nickpelling
We replace in the code the obscure expressions mapping files ABCDEFGH to ABCDDCBA
by an explicite call to an auxiliary function :
old: f = min(f, ~f)
new: f = map_to_queenside(f)
We used the Golbolt web site (https://godbolt.org) to find the optimal code
for the auxiliary function.
STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 30292 W: 6756 L: 6651 D: 16885
http://tests.stockfishchess.org/tests/view/5d8676720ebc5971531d6aa1
No functional change
This patch decreases the endgame scale factor using the 50 moves counter.
Looking at some games with this patch, it seems to have two effects on
the playing style:
1) when no progress can be made in late endgames (for instance in fortresses
or opposite bishops endgames) the evaluation will be largely tamed down
towards a draw value.
2) more interestingly, there is also a small effect in the midgame play because
Stockfish will panic a little bit if there are more than four consecutive
shuffling moves with an advantage: the engine will try to move a pawn or to
exchange a piece to keep the advantage, so the follow-ups of the position
will be discovered earlier by the alpha-beta search.
passed STC:
LLR: 2.95 (-2.94,2.94) [0.50,4.50]
Total: 23017 W: 5080 L: 4805 D: 13132
http://tests.stockfishchess.org/tests/view/5d7e4aef0ebc59069c36fc74
passed LTC:
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 30746 W: 5171 L: 4911 D: 20664
http://tests.stockfishchess.org/tests/view/5d7e513d0ebc59069c36ff26
Pull request: https://github.com/official-stockfish/Stockfish/pull/2304
Bench: 4272173
Follow-up to previous commit. Update the documentation for the user when using `make`,
to show the preferred bmi2 compile in the advanced examples section.
Note: I made a mistake in the previous commit comment, the documentation is shown when
using `make` or `make help`, not `make --help`.
No functional change
This reverts commit 33d9548218 ,
which crashed in DEBUG mode because of the following assert in position.h
````
Assertion failed: (is_ok(m)), function capture, file ./position.h, line 369.
````
No functional change
Official release version of Stockfish 10.
This is also the 10th anniversary version of the Stockfish project, which
started exactly ten years ago! I wish to extend a huge thank you to
all contributors and authors in our amazing community :-)
Bench: 3939338
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
Follow-up for the previous patch: we use an affine formula to mix stats
and evaluation in search. The idea is to give a bonus if the previous
move of the opponent was historically bad, and a malus if the previous
move of the opponent was historically good.
More precisely, if x is the stat score of the previous move by the opponent,
we implement the following formulas to tweak the evaluation at an internal
node of the tree for our pruning decisions at this node:
if x = 0, use v' = eval(P)
if x > 0, use v' = eval(P) - 5 - x/1024
if x < 0, use v' = eval(P) + 5 - x/1024
For reference, the previous master had this simpler rule:
if x > 0, use v' = eval(P) - 10
if x <= 0, use v' = eval(P)
STC:
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 29322 W: 6359 L: 6088 D: 16875
http://tests.stockfishchess.org/tests/view/5b76a5980ebc5902bdba957f
LTC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 30893 W: 5154 L: 4910 D: 20829
http://tests.stockfishchess.org/tests/view/5b76ca6d0ebc5902bdba9914
Closes https://github.com/official-stockfish/Stockfish/pull/1740
Bench: 4592766
We double in this patch the weight of the capture history table in the
local scoring of captures for move ordering.
The capture history table is indexed by the triplet (capturing piece,
capture square, captured piece) and gets information like "it seems to
have been historically good in that part of the search tree to capture
a pawn with a rook on g3, even if it seems to lose material", and affect
the normaly pure « Most Valuable Victim » ordering of captures.
Finished yellow at STC after 228842 games (posting a +1.36 Elo gain):
LLR: -2.95 (-2.94,2.94) [0.00,4.00]
Total: 228842 W: 50894 L: 50152 D: 127796
http://tests.stockfishchess.org/tests/view/5b714bb00ebc5902bdba332d
Passed LTC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 43251 W: 7425 L: 7131 D: 28695
http://tests.stockfishchess.org/tests/view/5b71c7d40ebc5902bdba3e51
Thanks to user Vizvezdenec for running the LTC test.
Closes https://github.com/official-stockfish/Stockfish/pull/1736
Bench: 4272361
This patch adds the tropism measure as a new term in the king danger variable.
Since we then trasform this variable as a Score via a quadratic formula, the
main effect of the patch is the positive correlation of the tropism measure
with some checks and pins information already present in the king danger code.
STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 6805 W: 1597 L: 1431 D: 3777
http://tests.stockfishchess.org/tests/view/5b5df8d10ebc5902bdb91699
LTC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 32872 W: 5782 L: 5523 D: 21567
http://tests.stockfishchess.org/tests/view/5b5e08d80ebc5902bdb917ee
How to continue from there?
• it may be possible to use CloseEnemies=S(7,0)
• we may want to try incorporating other strategic features in the quadratic
king danger.
Closes https://github.com/official-stockfish/Stockfish/pull/1717
Bench: 5591925
The previous commit wouldn't compile on the Microsoft Virtual Studio C++ compiler. So use a more compatible style for the same idea (which we already use in numerous places of evaluate.cpp, for instance in line 563).
Under the Clang compiler, both versions generate exactly the same machine code (same md5 signatures for the two binaries).
No functional change.
Remove a popcount for HinderPassedPawn, and compensate by doubling
the bonus from S(4,0) to to S(8,0).
Maybe it was pure luck, but we got the idea of this Elo gaining patch by
seing the simplification attempt by Mike Whiteley in pull request #1703.
This suggests that whenever we have a passed evaluation simplification,
we should consider the possibility that the master bonus has become
slightly out of tune with time, and we should try a few Elo gaining [0..4]
tests by hand-tuning the master bonus.
STC:
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 19136 W: 4388 L: 4147 D: 10601
http://tests.stockfishchess.org/tests/view/5b59be6f0ebc5902bdb8ac06
LTC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 99382 W: 17324 L: 16843 D: 65215
http://tests.stockfishchess.org/tests/view/5b59d2410ebc5902bdb8afa8
Closes https://github.com/official-stockfish/Stockfish/pull/1710
Bench: 4688817
This patch implements some idea by Alain Savard and Mike Whiteley taken from the perpertual renaming/reformatting thread.
This is a pure code cleaning patch (so no change in functionality), but I use it as a pretext to correct the bogus bench number that I introduced in the previous commit.
Bench: 4413383
Fix an error when compiling current master with MSVC due to the
ambiguity of which operator* overload was intended (reported by
Jarrod Torriero).
No functional change.
Simplifying away all the progressKey stuff gives exactly the same bench,
without any speed impact. Tested for speed against master with two benches
at depth 22 ran in parallel:
**testedpatch**
Total time (ms) : 92350
Nodes searched : 178962949
Nodes/second : 1937877
**master**
Total time (ms) : 92358
Nodes searched : 178962949
Nodes/second : 1937709
We also tested the patch at STC for no-regression with [-3, 1] bounds:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 57299 W: 11529 L: 11474 D: 34296
http://tests.stockfishchess.org/tests/view/5b015a1c0ebc5914abc126e5
Closes https://github.com/official-stockfish/Stockfish/pull/1603
No functional change.
Use the whole kingRing for pawn attackers instead of only the squares directly
around the king. This tends to give quite a lot more kingAttackersCount, so to
compensate and to avoid raising the king danger too fast we lower the values
in the KingAttackWeights array a little bit.
STC:
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 51892 W: 10723 L: 10369 D: 30800
http://tests.stockfishchess.org/tests/view/5af6d4dd0ebc5968e652428e
LTC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 24536 W: 3737 L: 3515 D: 17284
http://tests.stockfishchess.org/tests/view/5af709890ebc5968e65242ac
Credits to user @xoroshiro for the idea of using the kingRing for pawn attackers.
How to continue? It seems that the KingAttackWeights[] array stores values
which are quite Elo-sensitive, yet they have not been tuned with SPSA recently.
There might be easy Elo points to get there.
Closes https://github.com/official-stockfish/Stockfish/pull/1597
Bench: 5282815
When we are using the "Bitboard + Square" overloaded operators,
the compiler uses the interpediate SquareBB[s] to transform the
square into a Bitboard, and then calculate the result.
For instance, the following code:
```
b = pos.pieces(Us, PAWN) & s
```
generates in fact the code:
```
b = pos.pieces(Us, PAWN) & SquareBB[s]`
```
The bug introduced by Stéphane in the previous patch was the
use of `b = pos.pieces(Us, PAWN) & (s + Up)` which can result
in out-of-bounds errors for the SquareBB[] array if s in the
last rank of the board.
We coorect the bug, and also add some asserts in bitboard.h to
make the code more robust for this particular bug in the future.
Bug report by Joost VandeVondele. Thanks!
Bench: 5512000
Remove the distinction between the king file and the two neighbours
files in the ShelterStrength[] array. Instead we initialize the safety
variable in the evaluate_shelter() function with a -10 penalty if our
king is on a semi-open file (ie. if our king is on a file without a pawn
protection).
Also rename shelter_storm() to evaluate_shelter() while there.
STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 23153 W: 4795 L: 4677 D: 13681
http://tests.stockfishchess.org/tests/view/5adcb83d0ebc595ec7ff8aa7
LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 25728 W: 3934 L: 3821 D: 17973
http://tests.stockfishchess.org/tests/view/5adcdcb60ebc595ec7ff8adb
See the commit history in PR#1559 for the proof that the committed
version is equivalent to the version in the tests above:
https://github.com/official-stockfish/Stockfish/pull/1559
Full credit to @protonspring for the renormalized values of the
ShelterStrength[] array used for the simplification. Thanks!
Bench: 4703935
Change the operators of the Option type in uci.h to accept floating
point numbers in double precision on input as the numerical type for
the "spin" values of the UCI protocol.
The output of Stockfish after the "uci" command is unaffected.
This change is compatible with all the existing GUI (as they will
continue sending integers that we can interpret as doubles in SF),
and allows us to pass double parameters to Stockfish in the console
via the "setoption" command. This will be useful if we implement
another tuner as an alternative for SPSA.
Closes https://github.com/official-stockfish/Stockfish/pull/1556
No functional change.
---------------------
A example of the new functionality in action in the branch `tune_float2'`:
https://github.com/snicolet/Stockfish/commit/876c322d0f20ee232da977b4d3489c4cc929765e
I have added the following lines in ucioptions.cpp:
```C++
void on_pi(const Option& o)
{
double x = Options["PI"]; // or double x = o;
std::cerr << "received value is x = " << x << std::endl;
}
...
o["PI"] << Option(3.1415926, -10000000, 10000000, on_pi);
```
Then I can change the value of Pi in Stockfish via the command line, and
check that Stockfish understands a floating point:
````
> ./stockfish
> setoption name PI value 2.7182818284
received value is x = 2.71828
````
On output, the default value of Pi is truncated to 3 (to remain compatible
with the UCI protocol and GUIs):
````
> uci
[...]
option name SyzygyProbeLimit type spin default 6 min 0 max 6
option name PI type spin default 3 min -10000000 max 10000000
uciok
````
When we reach a position with only two opposite colored bishops and
one pawn on the board, current master would give it a scale factor
of 9/64=0.14 in about one position out of 7200, and a scale factor
of 0.0 in the 7199 others. The patch gives a scale factor of 0.0 in
100% of the cases.
STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 55845 W: 11467 L: 11410 D: 32968
http://tests.stockfishchess.org/tests/view/5abc585f0ebc5902926cf15e
LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 11915 W: 1852 L: 1719 D: 8344
http://tests.stockfishchess.org/tests/view/5abc7f750ebc5902926cf18c
We also have exhaustive coverage analysis of this patch effect by
Alain Savard, comparing the perfect evaluation given by the Syzygy
tablebase with the heuristic play after this patch for the set of
all legal positions of the KBPKP endgame with opposite bishops, in
the comments thread for this pull request:
https://github.com/official-stockfish/Stockfish/pull/1520
Alain's conclusion:
> According to this definition and the data, I consider this PR is
> identical to master to "solve for draw" and slightly better than
> master to solve earlier for "wins".
Note: this patch is a side effect of an ongoing effort to improve
the evaluation of positions involving a pair of opposite bishops.
See the GitHub diff of this LTC test which almost passed at sprt[0..5]
for a discussion:
http://tests.stockfishchess.org/tests/view/5ab9030b0ebc5902932cbf93
No functional change (at small bench depths)
This is a patch to fix issue #1498, switching the time management variables
to 64 bits to avoid overflow of time variables after 25 days.
There was a bug in Stockfish 9 causing the output to be wrong after
2^31 milliseconds search. Here is a long run from the starting position:
info depth 64 seldepth 87 multipv 1 score cp 23 nodes 13928920239402
nps 0 tbhits 0 time -504995523 pv g1f3 d7d5 d2d4 g8f6 c2c4 d5c4 e2e3 e7e6 f1c4
c7c5 e1g1 b8c6 d4c5 d8d1 f1d1 f8c5 c4e2 e8g8 a2a3 c5e7 b2b4 f8d8 b1d2 b7b6 c1b2
c8b7 a1c1 a8c8 c1c2 c6e5 d1c1 c8c2 c1c2 e5f3 d2f3 a7a5 b4b5 e7c5 f3d4 d8c8 d4b3
c5d6 c2c8 b7c8 b3d2 c8b7 d2c4 d6c5 e2f3 b7d5 f3d5 e6d5 c4e5 a5a4 e5d3 f6e4 d3c5
e4c5 b2d4 c5e4 d4b6 e4d6 g2g4 d6b5 b6c5 b5c7 g1g2 c7e6 c5d6 g7g6
We check at compile time that the TimePoint type is exactly 64 bits long for
the compiler (TimePoint is our alias in Stockfish for std::chrono::milliseconds
-- it is a signed integer type of at least 45 bits according to the C++ standard,
but will most probably be implemented as a 64 bits signed integer on modern
compilers), and we use this TimePoint type consistently across the code.
Bug report by user "fischerandom" on the TCEC chat (thanks), and the
patch includes code and suggestions by user "WOnder93" and Ronald de Man.
Fixes issue: https://github.com/official-stockfish/Stockfish/issues/1498
Closes pull request: https://github.com/official-stockfish/Stockfish/pull/1510
No functional change.
Implements renaming suggestions by Marco Costalba, Günther Demetz,
Gontran Lemaire, Ronald de Man, Stéphane Nicolet, Alain Savard,
Joost VandeVondele, Jerry Donald Watson, Mike Whiteley, xoto10,
and I hope that I haven't forgotten anybody.
Perpetual renaming thread for suggestions:
https://github.com/official-stockfish/Stockfish/issues/1426
No functional change.
We give a S(21,11) bonus for knight threats on the next moves
against enemy queen. The threats are from squares which are
"not strongly protected" and which may be empty, contain enemy
pieces or even one of our piece at the moment (N,B,Q,R) -- hence
be two-steps threats in the later case because we will have to
move our piece and *then* attack the enemy queen with the knight.
STC: http://tests.stockfishchess.org/tests/view/5a9e442e0ebc590297cb6162
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 35129 W: 7346 L: 7052 D: 20731
LTC: http://tests.stockfishchess.org/tests/view/5a9e6e620ebc590297cb617f
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 42442 W: 6695 L: 6414 D: 29333
How to continue from there?
• Trying to refine the threat condition ("not strongly protected")
• Trying the two-steps idea for bishops or rooks threats against queen
Bench: 6051247
The current master applies Eval::Tempo even to leaves evaluated
as draw by some of the static evaluation functions of endgame.cpp
(for instance KNN vs K or stalemates in KP vs K). This results in
some lines being reported as +0.07 or -0.07 when the terminal
position has reached such endgames (0.07 being about the value
of a tempo for Stockfish).
This patch does not apply Eval::tempo to these positions. This leads
to more nodes being evaluated as VALUE_DRAW during search, giving more
opportunities for cut-offs in alpha-beta.
STC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 52602 W: 11776 L: 11403 D: 29423
http://tests.stockfishchess.org/tests/view/5a8cb8f60ebc590297cc8546
LTC:
LLR: 2.97 (-2.94,2.94) [0.00,4.00]
Total: 156613 W: 26820 L: 26158 D: 103635
http://tests.stockfishchess.org/tests/view/5a8f452d0ebc590297cc865a
Bench: 4924749
The previous asymmetry measure of the pawn structure only used to
consider the number of pawns on semi-opened files in the position.
With this patch we also increase the measure by the number of passed
pawns for both players.
Many thanks to the community for the nice feedback on the previous
version, with special mentions to Alain Savard and Marco Costalba
for clarity and speed suggestions.
STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 13146 W: 3038 L: 2840 D: 7268
http://tests.stockfishchess.org/tests/view/5a91dd0c0ebc590297cc877e
LTC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 27776 W: 4771 L: 4536 D: 18469
http://tests.stockfishchess.org/tests/view/5a91fdd50ebc590297cc879b
How to continue after this patch?
Stockfish will now evaluate more positions with passed pawns, so
tuning the passed pawns values may bring Elo. The patch has also
consequences on the initiative term, where we might want to give
different weights to passed pawns and semi-openfiles (idea by
Stefano Cardanobile).
Bench: 5302866
