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Stockfish modified to play the worst move
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Joost VandeVondele 2cbc20e846 Correct and extend PV lines with decisive TB score
Currently (after #5407), SF has the property that any PV line with a decisive
TB score contains the corresponding TB position, with a score that correctly
identifies the depth at which TB are entered. The PV line that follows might
not preserve the game outcome, but can easily be verified and extended based on
TB information. This patch provides this functionality, simply extending the PV
lines on output, this doesn't affect search.

Indeed, if DTZ tables are available, search based PV lines that correspond to
decisive TB scores are verified to preserve game outcome, truncating the line
as needed. Subsequently, such PV lines are extended with a game outcome
preserving line until mate, as a possible continuation.  These lines are not
optimal mating lines, but are similar to what a user could produce on a website
like https://syzygy-tables.info/ clicking always the top ranked move, i.e.
minimizing or maximizing DTZ (with a simple tie-breaker for moves that have
identical DTZ), and are thus an just an illustration of how to game can be won.

A similar approach is already in established in
https://github.com/joergoster/Stockfish/tree/matefish2

This also contributes to addressing #5175 where SF can give an incorrect TB
win/loss for positions in TB with a movecounter that doesn't reflect optimal
play. While the full solution requires either TB generated differently, or a
search when ranking rootmoves, current SF will eventually find a draw in these
cases, in practice quite quickly, e.g.
`1kq5/q2r4/5K2/8/8/8/8/7Q w - - 96 1`
`8/8/6k1/3B4/3K4/4N3/8/8 w - - 54 106`

Gives the same results as master on an extended set of test positions from
9173d29c41
with the exception of the above mentioned fen where this commit improves.

With https://github.com/vondele/matetrack using 6men TB, all generated PVs verify:
```
Using ../Stockfish/src/stockfish.syzygyExtend on matetrack.epd with --nodes 1000000 --syzygyPath /chess/syzygy/3-4-5-6/WDL:/chess/syzygy/3-4-5-6/DTZ
Engine ID:     Stockfish dev-20240704-ff227954
Total FENs:    6555
Found mates:   3299
Best mates:    2582
Found TB wins: 568
```

As repeated DTZ probing could be slow a procedure (100ms+ on HDD, a few ms on
SSD), the extension is only done as long as the time taken is less than half
the `Move Overhead` parameter. For tournaments where these lines might be of
interest to the user, a suitable `Move Overhead` might be needed (e.g. TCEC has
1000ms already).

closes https://github.com/official-stockfish/Stockfish/pull/5414

No functional change
2024-07-05 15:43:49 +02:00
.github Use explicit action permissions in CI 2024-07-05 15:35:13 +02:00
scripts Fix dotprod detection 2024-01-17 18:32:20 +01:00
src Correct and extend PV lines with decisive TB score 2024-07-05 15:43:49 +02:00
tests Limit depth after extensions to avoid asserts. 2024-06-15 12:02:56 +02:00
.clang-format add clang-format 2023-10-22 16:06:27 +02:00
.git-blame-ignore-revs Add .git-blame-ignore-revs 2024-01-07 13:38:55 +01:00
.gitignore Add .gitignore 2021-01-30 13:19:20 +01:00
AUTHORS Remove the correction history bonus in null move search 2024-06-08 23:39:46 +02:00
CITATION.cff Add CITATION.cff file 2023-03-05 16:16:16 +01:00
CONTRIBUTING.md Update clang-format to version 18 2024-06-05 21:41:43 +02:00
Copying.txt Update links in license 2023-10-08 07:38:13 +02:00
README.md Simplify README 2023-09-03 08:40:08 +02:00
Top CPU Contributors.txt Update Top CPU Contributors 2024-02-24 17:58:44 +01:00

Stockfish

Stockfish

A free and strong UCI chess engine.
Explore Stockfish docs »

Report bug · Open a discussion · Discord · Blog

Build License
Release Commits
Website Fishtest Discord

Overview

Stockfish is a free and strong UCI chess engine derived from Glaurung 2.1 that analyzes chess positions and computes the optimal moves.

Stockfish does not include a graphical user interface (GUI) that is required to display a chessboard and to make it easy to input moves. These GUIs are developed independently from Stockfish and are available online. Read the documentation for your GUI of choice for information about how to use Stockfish with it.

See also the Stockfish documentation for further usage help.

Files

This distribution of Stockfish consists of the following files:

  • README.md, the file you are currently reading.

  • Copying.txt, a text file containing the GNU General Public License version 3.

  • AUTHORS, a text file with the list of authors for the project.

  • src, a subdirectory containing the full source code, including a Makefile that can be used to compile Stockfish on Unix-like systems.

  • a file with the .nnue extension, storing the neural network for the NNUE evaluation. Binary distributions will have this file embedded.

Contributing

See Contributing Guide.

Donating hardware

Improving Stockfish requires a massive amount of testing. You can donate your hardware resources by installing the Fishtest Worker and viewing the current tests on Fishtest.

Improving the code

In the chessprogramming wiki, many techniques used in Stockfish are explained with a lot of background information. The section on Stockfish describes many features and techniques used by Stockfish. However, it is generic rather than focused on Stockfish's precise implementation.

The engine testing is done on Fishtest. If you want to help improve Stockfish, please read this guideline first, where the basics of Stockfish development are explained.

Discussions about Stockfish take place these days mainly in the Stockfish Discord server. This is also the best place to ask questions about the codebase and how to improve it.

Compiling Stockfish

Stockfish has support for 32 or 64-bit CPUs, certain hardware instructions, big-endian machines such as Power PC, and other platforms.

On Unix-like systems, it should be easy to compile Stockfish directly from the source code with the included Makefile in the folder src. In general, it is recommended to run make help to see a list of make targets with corresponding descriptions. An example suitable for most Intel and AMD chips:

cd src
make -j profile-build ARCH=x86-64-avx2

Detailed compilation instructions for all platforms can be found in our documentation. Our wiki also has information about the UCI commands supported by Stockfish.

Terms of use

Stockfish is free and distributed under the GNU General Public License version 3 (GPL v3). Essentially, this means you are free to do almost exactly what you want with the program, including distributing it among your friends, making it available for download from your website, selling it (either by itself or as part of some bigger software package), or using it as the starting point for a software project of your own.

The only real limitation is that whenever you distribute Stockfish in some way, you MUST always include the license and the full source code (or a pointer to where the source code can be found) to generate the exact binary you are distributing. If you make any changes to the source code, these changes must also be made available under GPL v3.