Ply (game theory)
In two-or-more-player sequential games, a ply is one turn taken by one of the players. The word is used to clarify what is meant when one might otherwise say "turn".
The word "turn" can be a problem since it means different things in different traditions. For example, in standard chess terminology, one move consists of a turn by each player; therefore a ply in chess is a half-move. Thus, after 20 moves in a chess game, 40 plies have been completed—20 by white and 20 by black. In the game of Go, by contrast, a ply is the normal unit of counting moves; so for example to say that a game is 250 moves long is to imply 250 plies.
In poker with n players the word "street" is used for a full betting round consisting of n plies; each dealt card may sometimes also be called a "street". For instance, in heads up
The word "ply" used as a synonym for "layer" goes back to the 15th century.[2] Arthur Samuel first used the term in its game-theoretic sense in his seminal paper on machine learning in checkers in 1959,[3] but with a slightly different meaning: the "ply", in Samuel's terminology, is actually the depth of analysis ("Certain expressions were introduced which we will find useful. These are: Ply, defined as the number of moves ahead, where a ply of two consists of one proposed move by the machine and one anticipated reply by the opponent"[4]).
In computing, the concept of a ply is important because one ply corresponds to one level of the
See also
- Minimax algorithm
References
- ^ Chen, Bill and Ankenman, Jerrod. The Mathematics of Poker, p110
- ^ Online Etymology Dictionary, "ply" (cited 24 April 2011)
- ^ A.L. Samuel, March 3, 1959: Some Studies in Machine Learning Using the Game of Checkers (cited 25 August 2006)
- ^ A.L. Samuel, March 3, 1959: Some Studies in Machine Learning Using the Game of Checkers, p. 601 (cited 2 May 2018)
- S2CID 662187.
Further reading
- ISBN 978-0-7167-8121-9
External links
The dictionary definition of ply at Wiktionary