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Subject: Re: Board games and mathematical complexity: a poll

Author: Bruce Cleaver

Date: 09:58:02 12/11/02

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On December 11, 2002 at 12:45:59, GuyHaworth wrote:

>H.J. van den Herik, J.W.H.M.Uiterwijk and J. van Rijswijck, in a paper:
>
>"Games Solved: Now and in the Future"
>
>give a table (Table 6) of the 'state-space complexity' and 'Game-tree
>complexity' [i.e. the number of positions and number of games] of some 18 games
>... in alpha-order:
>
>  Awari, Checkers, Chess, Chinese Chess, Connect-Four, Dakon-6,
>  Domineering (8x8), Draughts, Go (19x19), Go-Moku (15x15), Hex (11x11),
>  Kalah (6, 4), Nine Men's Morris, Othello, Pentominoes, Qubic, Renju (15x15),
>  Shogi
>
>Some of these like Connect-Four, Dakon-6, Domineering (for many board-sizes),
>Go-Moku (some variants), Hex (to 6x6 if not 6x7 boards), Kalah, Qubic and Renju
>have been 'weakly-solved', i.e. given a 'theoretical game-value' for the initial
>position.
>
>The authors address the question of the 'intrinsic difficulty of the game', for
>which the state-space and game-tree complexity numbers give a rough indication.
>
>However, it has to be admitted that there is a game with arbitrarily large
>state-space and game-tree figures which is not complex at all but trivial to
>evaluate, namely, Nim.
>
>The numbers following are the power of 10 for the 'state-space complexity' and
>'game-tree complexity' of the games:
>
>                    state, game
>
>  Awari               12    32
>  Checkers            21    31
>  Chess               46   123
>  Chinese Chess       48   150
>  Connect-Four        14    21
>  Dakon-6             15    33
>  Domineering (8x8)   15    27
>  Draughts            30    54
>  Go (19x19)         172   360
>  Go-Moku (15x15)    105    70
>  Hex (11x11)         57    98
>  Kalah (6, 4)        13    18
>  Nine Men's Morris   10    50
>  Othello             28    58
>  Pentominoes         12    18
>  Qubic               30    34
>  Renju (15x15)      105    70
>  Shogi               71   226
>
>As the counter-example of Nim shows, these figures are not necessarily
>correlated with the difficulty of solving the game or writing a program.
>
>But the survey is perhaps the most comprehensive done cross game-domains so far:
>
>Artificial Intelligence, v134 (2002) p. 277-311.
>
>Reprinted in "Chips Challenging Champions", Elsevier (2002),
>(eds. J. Schaeffer and J. van den Herik)
>ISBN 0-444-50949-6

Thanks for posting this - I have seen estimates of some games in some places,
but not conveniently gathered together.  Go is very hard not only for its large
state space, but because material differences appear to be unimportant (unlike
chess where being a piece up USUALLY means you win).  Connect-4 has been solved
completely by Victor Allis in his PhD dissertation.  First player wins.



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