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

Author: GuyHaworth

Date: 09:45:59 12/11/02

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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




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