![]() This patch applies a S(10, 5) bonus for every square that is: - Occupied by an enemy piece which is not a pawn - Attacked exactly once by our pieces - Defended exactly once by enemy pieces The idea is that these pieces must be defended. Their defenders have dramatically limited mobility, and they are vulnerable to our future attack. As with connectivity, there are probably many more tests to be run in this area. In particular: - I believe @snicolet's queen overload tests have demonstrated a potential need for a queen overload bonus above and beyond this one; however, the conditions for "overload" in this patch are different (excluding pieces we attack twice). My next test after this is (hopefully) merged will be to intersect the Bitboard I define here with the enemy's queen attacks and attempt to give additional bonus. - Perhaps we should exclude pieces attacked by pawns--can pawns really be overloaded? Should they have the same weight, or less? This didn't work with a previous version, but it could work with this one. - More generally, different pieces may need more or less bonus. We could change bonuses based on what type of enemy piece is being overloaded, what type of friendly piece is attacking, and/or what type of piece is being defended by the overloaded piece and attacked by us, or any intersection of these three. For example, here attacked/defended pawns are excluded, but they're not totally worthless targets, and could be added again with a smaller bonus. - This list is by no means exhaustive. STC: LLR: 2.96 (-2.94,2.94) [0.00,5.00] Total: 17439 W: 3599 L: 3390 D: 10450 http://tests.stockfishchess.org/tests/view/5ac78a2e0ebc59435923735e LTC: LLR: 2.95 (-2.94,2.94) [0.00,5.00] Total: 43304 W: 6533 L: 6256 D: 30515 http://tests.stockfishchess.org/tests/view/5ac7a1d80ebc59435923736f Closes https://github.com/official-stockfish/Stockfish/pull/1533 Bench: 5248871 ---------------- This is my first time opening a PR, so I apologize if there are errors. There are too many people to thank since I submitted my first test just over a month ago. Thank you all for the warm welcome and here is to more green patches! In particular, I would like to thank: - @crossbr, whose comment in a FishCooking thread first inspired me to consider the overloading of pieces other than queens, - @snicolet, whose queen overload tests inspired this one and served as the base of my first overload attempts, - @protonspring, whose connectivity tests inspired this one and who provided much of the feedback needed to take this from red to green, - @vondele, who kindly corrected me when I submitted a bad LTC test, - @Rocky640, who has helped me over and over again in the past month. Thank you all! |
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Readme.md | ||
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appveyor.yml |
Readme.md
Overview
Stockfish is a free UCI chess engine derived from Glaurung 2.1. It is not a complete chess program and requires some UCI-compatible GUI (e.g. XBoard with PolyGlot, eboard, Arena, Sigma Chess, Shredder, Chess Partner or Fritz) in order to be used comfortably. Read the documentation for your GUI of choice for information about how to use Stockfish with it.
This version of Stockfish supports up to 512 cores. The engine defaults to one search thread, so it is therefore recommended to inspect the value of the Threads UCI parameter, and to make sure it equals the number of CPU cores on your computer.
This version of Stockfish has support for Syzygybases.
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.
-
src, a subdirectory containing the full source code, including a Makefile that can be used to compile Stockfish on Unix-like systems.
Syzygybases
Configuration
Syzygybases are configured using the UCI options "SyzygyPath", "SyzygyProbeDepth", "Syzygy50MoveRule" and "SyzygyProbeLimit".
The option "SyzygyPath" should be set to the directory or directories that contain the .rtbw and .rtbz files. Multiple directories should be separated by ";" on Windows and by ":" on Unix-based operating systems. Do not use spaces around the ";" or ":".
Example: C:\tablebases\wdl345;C:\tablebases\wdl6;D:\tablebases\dtz345;D:\tablebases\dtz6
It is recommended to store .rtbw files on an SSD. There is no loss in storing the .rtbz files on a regular HD.
Increasing the "SyzygyProbeDepth" option lets the engine probe less aggressively. Set this option to a higher value if you experience too much slowdown (in terms of nps) due to TB probing.
Set the "Syzygy50MoveRule" option to false if you want tablebase positions that are drawn by the 50-move rule to count as win or loss. This may be useful for correspondence games (because of tablebase adjudication).
The "SyzygyProbeLimit" option should normally be left at its default value.
What to expect If the engine is searching a position that is not in the tablebases (e.g. a position with 7 pieces), it will access the tablebases during the search. If the engine reports a very large score (typically 123.xx), this means that it has found a winning line into a tablebase position.
If the engine is given a position to search that is in the tablebases, it will use the tablebases at the beginning of the search to preselect all good moves, i.e. all moves that preserve the win or preserve the draw while taking into account the 50-move rule. It will then perform a search only on those moves. The engine will not move immediately, unless there is only a single good move. The engine likely will not report a mate score even if the position is known to be won.
It is therefore clear that behaviour is not identical to what one might be used to with Nalimov tablebases. There are technical reasons for this difference, the main technical reason being that Nalimov tablebases use the DTM metric (distance-to-mate), while Syzygybases use a variation of the DTZ metric (distance-to-zero, zero meaning any move that resets the 50-move counter). This special metric is one of the reasons that Syzygybases are more compact than Nalimov tablebases, while still storing all information needed for optimal play and in addition being able to take into account the 50-move rule.
Compiling it yourself
On Unix-like systems, it should be possible to compile Stockfish directly from the source code with the included Makefile.
Stockfish has support for 32 or 64-bit CPUs, the hardware POPCNT instruction, big-endian machines such as Power PC, and other platforms.
In general it is recommended to run make help
to see a list of make
targets with corresponding descriptions. When not using the Makefile to
compile (for instance with Microsoft MSVC) you need to manually
set/unset some switches in the compiler command line; see file types.h
for a quick reference.
Resource For Understanding the Code Base
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Chess Programming Wiki has good overall chess engines explanations (techniques used here are well explained like hash maps etc), it was also recommended by the support team at stockfish.
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Here you can find a set of features and techniques used by stockfish and each of them is explained at the wiki, however, it's a generic way rather than focusing on stockfish's own implementation, but it will still help you.
Terms of use
Stockfish is free, and distributed under the GNU General Public License (GPL). Essentially, this means that 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 web site, 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 full source code, or a pointer to where the source code can be found. If you make any changes to the source code, these changes must also be made available under the GPL.
For full details, read the copy of the GPL found in the file named Copying.txt.