Chess Position

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The Chess Position describes how pieces are placed on the chessboard, as printed as chess diagram, image or photograph from a game of chess. In 1996 Shirish Chinchalkar determined 1046 as upper bound for the number of reachable chess positions [3]. The maximum number of moves per chess position seems 218 [4].

Of course, the information of any arbitrary chess position which occurs inside the game of chess, might be determined from a certain initial starting position and a sequence of moves (half-moves), which leads to this position. Anyway, an efficient data structure for a chess position, which is incrementally updated during game play and search is essential for a chess playing program.

Specifying a Chess Position

Except the determination of three fold repetitions, which requires the whole move record, at least from the last irreversible move (half-move) played, the chess position should keep track of various informations related to the position also for efficiency reasons. Another issue is to make chess positions persistent with a maximum of information required, but without the whole game history, as specified by the Forsyth-Edwards Notation or Extended Position Description.

Beside piece placement, as considered by the board representation, the side to move is essential, which might take only one bit inside an appropriate data structure for a chess position. Additionally, the Castling ability for both sides, as reflected by the castling rights and a possible en passant target square (or file) is needed to further completely specify the position, as well as the halfmove clock to cover the fifty-move rule.


A chess positions consists of

Positions inside the Search

In the context of Search, a position is the node inside a search tree. To completely determine the position with respect to repetitions, one additionally needs a move list or any other appropriate data structure, to keep up to 100 reversible half-moves, likely associated with Zobrist keys of the intermediate positions.



Flipping and Mirroring

See Also

Piece Recognition


Forum Posts

1980 ...

1990 ...

Re: number of moves in position by Leonid, CCC, September 21, 1999

2000 ...

2010 ...

2015 ...

2020 ...

Re: On the number of chess positions by John Tromp, CCC, April 02, 2022
Re: On the number of chess positions by Peter Österlund, CCC, April 03, 2022 » Retrograde Analysis

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