KnightCap is an open source
computer
A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...
chess engine
In computer chess, a chess engine is a computer program that analyzes chess or chess variant positions, and generates a move or list of moves that it regards as strongest.
A chess engine is usually a back end with a command-line interface wit ...
. Its primary author is
Andrew Tridgell
Andrew "Tridge" Tridgell (born 28 February 1967) is an Australian computer programmer. He is the author of and a contributor to the Samba file server, and co-inventor of the rsync algorithm.
He has analysed complex proprietary protocols and a ...
and it was created circa 1996. Major contributions have also been made by
Jon Baxter and probably minor contributions by a few others. KnightCap is
free software
Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, no ...
released under the
GNU GPL
The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general us ...
.
In most ways, KnightCap is a fairly typical modern program. It uses
bitboard
A bitboard is a specialized bit array data structure commonly used in computer systems that play board games, where each bit corresponds to a game board space or piece. This allows parallel bitwise operations to set or query the game state, or de ...
data structures that are slightly different from those that were well known in 1996, but obvious enough and probably well known now. There is backward pruning using
MTD(f)
MTD(f) is an alpha-beta game tree search algorithm modified to use ‘zero-window’ initial search bounds, and memory (usually a transposition table) to reuse intermediate search results. MTD(f) is a shortened form of MTD(n,f) which stands for Me ...
(a method approximately equivalent to
Alpha-beta pruning Alphabeta is an Israeli musical group. Alphabeta or Alpha Beta may also refer to:
*The Greek alphabet, from ''Alpha'' (Αα) and ''Beta'' (Ββ), the first two letters
*Alpha Beta, a former chain of Californian supermarkets
*Alpha and beta anomers ...
but slightly more efficient in some settings). There is
Null-move heuristic In computer chess programs, the null-move heuristic is a heuristic (computer science), heuristic technique used to enhance the speed of the alpha-beta pruning search algorithm, algorithm.
Rationale
Alpha-beta pruning speeds the minimax algorithm ...
. There is a fairly complex end-node evaluation process that considers similar features to other programs.
In addition, KnightCap has support for multi-processor computers, in particular the now obsolete
Fujitsu CAP computer
research machines.
The most original feature of KnightCap, introduced in the late 1990s, was an experiment in
temporal difference learning
Temporal difference (TD) learning refers to a class of model-free reinforcement learning methods which learn by bootstrapping from the current estimate of the value function. These methods sample from the environment, like Monte Carlo methods, a ...
as applied to chess. This technique allowed KnightCap to automatically tune the weights applied to the various features in its
evaluation function
An evaluation function, also known as a heuristic evaluation function or static evaluation function, is a function used by game-playing computer programs to estimate the value or goodness of a position (usually at a leaf or terminal node) in a g ...
based on the games it played.
For a while in the 1990s, KnightCap was quite active on
chess servers
An Internet chess server (ICS) is an external Server (computing), server that provides the facility to play, discuss, and view the board game of chess over the Internet. The term specifically refers to facilities for connecting players through a va ...
on the Internet, but it is now semi-retired and rarely seen. Its strength is below that of the strongest programs, but still quite good.{{Fact, date=February 2007
External links
KnightCap's home pageKnightCap: A Chess program that learns by combining TD(λ) with minimax search
Chess engines
Free chess software