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Intelligence Artificial Intelligence Ian Gent Game Playing: Checkers.

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Presentation on theme: "Intelligence Artificial Intelligence Ian Gent Game Playing: Checkers."— Presentation transcript:

1 Intelligence Artificial Intelligence Ian Gent Game Playing: Checkers

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

3 3 A Checkered History zArthur Samuel, 1959 yLearning algorithm used to build computer checkers player yBeat a master zPatrick Prosser, 1970s yUndergraduate project yProbably state of the art at that time yNot developed further zJonathan Schaeffer, 1990s yChinook is the World Man-Machine champion yPossibly the best player there has ever been of any kind

4 4 Further Reading zJ Schaeffer yOne Jump Ahead xSpringer, 1997 xA popular account of the history of Chinook xLittle technical detail zJ Schaeffer, J Culberson, N Treloar, B Knight, P Lu, D Szafron yA world championship caliber checkers program xArtificial Intelligence, Vol 53, pages , 1992

5 5 Didnt Samuel solve Checkers? zSamuels programs opponent made an appalling move…

6 6 Prehistory of Chinook zJoe Culberson: yWhat is the real size of the search tree in Checkers? yNot the naïve estimate of zJonathan Schaeffer took up the challenge zProject began June 1989 yGoals were to beat Marion Tinsley yand solve the game completely

7 7 History of Chinook zTournament August 1990 yUS National Open, 2nd to Marion Tinsley yGained right to challenge Tinsley for World Title zPolitical shenanigans yEstablishment did not want machine to be champion yTinsley resigned championship to be able to play Chinook yfudge was World Man Machine Championship zMatch vs Tinsley, August 1992 yLost to Tinsley, won 2, lost 4, drawn 33

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

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

10 10 Search in Checkers zWhat is the search tree like in Checkers? zIt is possible to get Zugzwang -- every move loses zFine line between win and draw ye.g. textbook example with 40 critical moves required zCaptures are forced, reducing branching rate yabout 8 when no captures, about 1.25 when captures zEndgame databases heavily used yChinook can use the endgame database at the root

11 11 Search in Checkers zSearch early in the game involves all of … yopening ymiddlegame yendgame yendgame database zAll of these factors make search different from chess

12 Intelligence Artificial Intelligence 1. History 2.Search in Checkers 3. Endgame Databases 4. Chinook The Story of the Worlds Best Draughts Player 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 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

13 13 Endgame Databases zEndgames can be 100 moves long in checkers ybranching rate of 2 gives = positions. zBut there is a trick when few pieces left yfirst used by Ken Thompson in Chess x(Ken Thompson wrote first Unix, won Turing award) zCalculate the true optimal move for every position ye.g. 406 x 10 9 eight piece positions, 4x10 11 << zBest version of Chinook used 8 piece databases yweb version just uses 6 piece

14 14 How to calculate Endgame DBs z0. Duplicate every position, for W/B to move z1. Try every possible position of the pieces yMark as Win/0 if W has won in this position yMark as Loss/0 if W has lost in this position yLeave other positions unmarked z2. Iterate until no new positions are marked y2a) Try every unmarked position of the pieces xIf W has move to Win/n, mark as Win/n+1 xIf 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 Ian Gent: Of course W might have move to Loss/1, Loss/3, Loss/5. In this case n = 5

15 15 Calculating Endgame Databases zWhen this process has finished yWe know the number of moves to win for every position xwhere either B or W can force win yTherefore every other position must be drawn zso the following is valid z3. Mark all unmarked positions as Drawn zWe can calculate optimal winning moves yIn Win/n position, best move for W is to any Win/n-1 yin Drawn, best move for W is to any Drawn position, yIn Loss/n position, best move is to Loss/n-1

16 Intelligence Artificial Intelligence 1. History 2.Search in Checkers 3. Endgame Databases 4. Chinook: Putting it all together The Story of the Worlds Best Draughts Player 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 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

17 17 Putting it all together zStandard techniques search yendgame databases zvariable search depth xe.g. pursue positions with material deficit less deeply zAn AntiBook ynot a standard opening book known to opponents ya book of disallowed moves, encouraging novelty

18 18 Static Evaluation function zGame divided into 5 phases yopening ymiddlegame yearly endgame ylate endgame yendgame database zDifferent evaluation function at each stage zSearch involves all phases early in the game ydeal with blemish effect by rescaling each phase I.e. problem that score jumps as move from one phase to next

19 19 Static Evaluation function zGame divided into 5 phases yopening ymiddlegame yearly endgame ylate endgame yendgame database zDifferent evaluation function … zSearch involves all phases … ydeal with blemish effect by rescaling... zTotal is 88 parameters plus scaling factors! 22 parameters perfect info. 88 parameters scaling factors

20 20 The Weigh-in

21 21 The Present and the Future zPresent yChinook is best player in the world following Tinsley yNever beat Tinsley in a match, not near solving Checkers yDeep Blue beat Kasparov, but has been dismantled zHarder games yGo: huge branching rate (computers terrible) yBridge: uncertainty yCivilization: worst of both the above!


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