4c4cb185aa
This patch decays a little the evaluation (up to a few percent) for positions which have a large complexity measure (material imbalance, positional compensations, etc). This may have nice consequences on the playing style, as it modifies the search differently for attack and defense, both effects being desirable: - to see the effect on positions when Stockfish is defending, let us suppose for instance that the side to move is Stockfish and the nnue evaluation on the principal variation is -100 : this patch will decay positions with an evaluation of -103 (say) to the same level, provided they have huge material imbalance or huge positional compensation. In other words, chaotic positions with an evaluation of -103 are now comparable in our search tree to stable positions with an evaluation of -100, and chaotic positions with an evaluation of -102 are now preferred to stable positions with an evaluation of -100. - the effect on positions when Stockfish is attacking is the opposite. Let us suppose for instance that the side to move is Stockfish and the nnue evaluation on the principal variation is +100 : this patch will decay the evaluation to +97 if the positions on the principal variation have huge material imbalance or huge positional compensation. In other words, stable positions with an evaluation of +97 are now comparable in our search tree to chaotic positions with an evaluation of +100, and stable positions with an evaluation of +98 are now preferred to chaotic positions with an evaluation of +100. So the effect of this small change of evaluation on the playing style is that Stockfish should now play a little bit more turbulent when defending, and choose slightly simpler lines when attacking. passed STC: LLR: 2.93 (-2.94,2.94) <0.00,2.00> Total: 268448 W: 68713 L: 68055 D: 131680 Ptnml(0-2): 856, 31514, 68943, 31938, 973 https://tests.stockfishchess.org/tests/view/64e252bb99700912526653ed passed LTC: LLR: 2.94 (-2.94,2.94) <0.50,2.50> Total: 141060 W: 36066 L: 35537 D: 69457 Ptnml(0-2): 71, 15179, 39522, 15666, 92 https://tests.stockfishchess.org/tests/view/64e4447a9009777747553725 closes https://github.com/official-stockfish/Stockfish/pull/4762 Bench: 1426295 |
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|---|---|---|
| .github | ||
| src | ||
| tests | ||
| .gitignore | ||
| AUTHORS | ||
| CITATION.cff | ||
| Copying.txt | ||
| README.md | ||
| Top CPU Contributors.txt | ||
Stockfish
A free and strong UCI chess engine.
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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:
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README.md, the file you are currently reading.
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Copying.txt, a text file containing the GNU General Public License version 3.
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AUTHORS, a text file with the list of authors for the project.
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src, a subdirectory containing the full source code, including a Makefile that can be used to compile Stockfish on Unix-like systems.
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a file with the .nnue extension, storing the neural network for the NNUE evaluation. Binary distributions will have this file embedded.
The UCI protocol
The Universal Chess Interface (UCI) is a standard text-based protocol used to communicate with a chess engine and is the recommended way to do so for typical graphical user interfaces (GUI) or chess tools. Stockfish implements the majority of its options.
Developers can see the default values for the UCI options available in Stockfish
by typing ./stockfish uci in a terminal, but most users should typically use a
chess GUI to interact with Stockfish.
For more information on UCI or debug commands, see our documentation.
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.
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.
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.