1 / 21

Artificial Intelligence

Artificial Intelligence. Game Playing: Checkers. Ian Gent ipg@cs.st-and.ac.uk. Ian Gent: Why not chess? Unfortunately there has not been a good article or book written about Deep Blue. There is a good journal article and a book about Chinook, the checkers program.

arden
Télécharger la présentation

Artificial Intelligence

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Artificial Intelligence Game Playing: Checkers Ian Gent ipg@cs.st-and.ac.uk

  2. Ian Gent: Why not chess? Unfortunately there has not been a good article or book written about Deep Blue. There is a good journal article and a book about Chinook, the checkers program Artificial Intelligence The Story of the World’s Best Draughts Player 1. History 2. Search in Checkers 3. Endgame Databases 4. Chinook

  3. A Checkered History • Arthur Samuel, 1959 • Learning algorithm used to build computer checkers player • Beat a ‘master’ • Patrick Prosser, 1970s • Undergraduate project • Probably state of the art at that time • Not developed further • Jonathan Schaeffer, 1990s • Chinook is the World Man-Machine champion • Possibly the best player there has ever been of any kind

  4. Further Reading • J Schaeffer • One Jump Ahead • Springer, 1997 • A popular account of the history of Chinook • Little technical detail • J Schaeffer, J Culberson, N Treloar, B Knight, P Lu, D Szafron • A world championship caliber checkers program • Artificial Intelligence, Vol 53, pages 273-289, 1992

  5. Didn’t Samuel solve Checkers? • Samuel’s program’s opponent made an appalling move…

  6. Prehistory of Chinook • Joe Culberson: • What is the real size of the search tree in Checkers? • Not the naïve estimate of 1040 • Jonathan Schaeffer took up the challenge • Project began June 1989 • Goals were to beat Marion Tinsley • and solve the game completely

  7. History of Chinook • Tournament August 1990 • US National Open, 2nd to Marion Tinsley • Gained right to challenge Tinsley for World Title • Political shenanigans • Establishment did not want machine to be champion • Tinsley resigned championship to be able to play Chinook • fudge was “World Man Machine Championship” • Match vs Tinsley, August 1992 • Lost to Tinsley, won 2, lost 4, drawn 33

  8. History of Chinook • World Man Machine Championship, August 1994 • vs Tinsley, drew 6, won 0, lost 0 • won title by forfeit when Tinsley fell ill -- died 1995 • World Man Machine Championship, 1995 • vs Don Lafferty, won 1, lost 0, drew 31 • Play it on the Web today! • http://www.cs.ualberta.ca/~chinook/play.html

  9. Artificial Intelligence The Story of the World’s Best Draughts Player 1. History 2. Search in Checkers 3. Endgame Databases 4. Chinook

  10. Search in Checkers • What is the search tree like in Checkers? • It is possible to get Zugzwang -- every move loses • Fine line between win and draw • e.g. textbook example with 40 critical moves required • Captures are forced, reducing branching rate • about 8 when no captures, about 1.25 when captures • Endgame databases heavily used • Chinook can use the endgame database at the root

  11. Search in Checkers • Search early in the game involves all of … • opening • middlegame • endgame • endgame database • All of these factors make search different from chess

  12. Ian Gent: Why not chess? Unfortunately there has not been a good article or book written about Deep Blue. There is a good journal article and a book about Chinook, the checkers program Artificial Intelligence The Story of the World’s Best Draughts Player 1. History 2. Search in Checkers 3. Endgame Databases 4. Chinook

  13. Endgame Databases • Endgames can be 100 moves long in checkers • branching rate of 2 gives 2100 = 1030 positions. • But there is a trick when few pieces left • first used by Ken Thompson in Chess • (Ken Thompson wrote first Unix, won Turing award) • Calculate the true optimal move for every position • e.g. 406 x 109 eight piece positions, 4x1011<< 1030 • Best version of Chinook used 8 piece databases • web version just uses 6 piece

  14. How to calculate Endgame DB’s • 0. Duplicate every position, for W/B to move • 1. Try every possible position of the pieces • Mark as Win/0 if W has won in this position • Mark as Loss/0 if W has lost in this position • Leave other positions unmarked • 2. Iterate until no new positions are marked • 2a) Try every unmarked position of the pieces • If W has move to Win/n, mark as Win/n+1 • If every W move is to Loss/n, mark as Loss/n+1 Ian Gent: Of course W might have move to Loss/1, Loss/3, Loss/5. In this case n = 5

  15. Calculating Endgame Databases • When this process has finished • We know the number of moves to win for every position • where either B or W can force win • Therefore every other position must be drawn • so the following is valid • 3. Mark all unmarked positions as Drawn • We can calculate optimal winning moves • In Win/n position, best move for W is to any Win/n-1 • in Drawn, best move for W is to any Drawn position, • In Loss/n position, best move is to Loss/n-1

  16. Ian Gent: Why not chess? Unfortunately there has not been a good article or book written about Deep Blue. There is a good journal article and a book about Chinook, the checkers program Artificial Intelligence The Story of the World’s Best Draughts Player 1. History 2. Search in Checkers 3. Endgame Databases 4. Chinook: Putting it all together

  17. Putting it all together • Standard techniques • a-b search • endgame databases • variable search depth • e.g. pursue positions with material deficit less deeply • An AntiBook • not a standard opening book known to opponents • a book of disallowed moves, encouraging novelty

  18. Static Evaluation function • Game divided into 5 phases • opening • middlegame • early endgame • late endgame • endgame database • Different evaluation function at each stage • Search involves all phases early in the game • deal with ‘blemish effect’ by rescaling each phase • I.e. problem that score jumps as move from one phase to next

  19. Static Evaluation function • Game divided into 5 phases • opening • middlegame • early endgame • late endgame • endgame database • Different evaluation function … • Search involves all phases … • deal with ‘blemish effect’ by rescaling ... • Total is 88 parameters plus scaling factors! 22 parameters 22 parameters 22 parameters 22 parameters perfect info. 88 parameters scaling factors

  20. The Weigh-in

  21. The Present and the Future • Present • Chinook is best player in the world following Tinsley • Never beat Tinsley in a match, not near solving Checkers • Deep Blue beat Kasparov, but has been dismantled • Harder games • Go: huge branching rate (computers terrible) • Bridge: uncertainty • Civilization: worst of both the above!

More Related