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.IX Title "Games::AlphaBeta 3"
.TH Games::AlphaBeta 3 "2008-01-05" "perl v5.8.8" "User Contributed Perl Documentation"
.SH "NAME"
Games::AlphaBeta \- game\-tree search with object oriented interface
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&    package My::GamePos;
\&    use base qw(Games::AlphaBeta::Position);
.Ve
.PP
.Vb 2
\&    # initialise starting position
\&    sub _init { ... }
.Ve
.PP
.Vb 5
\&    # Methods required by Games::AlphaBeta
\&    sub apply { ... }
\&    sub endpos { ... }          # optional
\&    sub evaluate { ... }
\&    sub findmoves { ... }
.Ve
.PP
.Vb 2
\&    # Draw a position in the game (optional)
\&    sub draw { ... }
.Ve
.PP
.Vb 3
\&    package main;
\&    my $pos = My::GamePos->new;
\&    my $game = Games::AlphaBeta->new($pos);
.Ve
.PP
.Vb 3
\&    while ($game->abmove) {
\&        print draw($game->peek_pos);
\&    }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Games::AlphaBeta provides a generic implementation of the
AlphaBeta game-tree search algorithm (also known as MiniMax
search with alpha beta pruning). This algorithm can be used to
find the best move at a particular position in any two\-player,
zero-sum game with perfect information. Examples of such games
include Chess, Othello, Connect4, Go, Tic-Tac-Toe and many, many
other boardgames. 
.PP
Users must pass an object representing the initial state of the
game as the first argument to \f(CW\*(C`new()\*(C'\fR. This object must provide
the following methods: \f(CW\*(C`copy()\*(C'\fR, \f(CW\*(C`apply()\*(C'\fR, \f(CW\*(C`endpos()\*(C'\fR,
\&\f(CW\*(C`evaluate()\*(C'\fR and \f(CW\*(C`findmoves()\*(C'\fR. This is explained more
carefully in Games::AlphaBeta::Position which is a base class
you can use to implement your position object.
.SH "INHERITED METHODS"
.IX Header "INHERITED METHODS"
The following methods are inherited from Games::Sequential:
.IP "new" 4
.IX Item "new"
.PD 0
.IP "debug" 4
.IX Item "debug"
.IP "peek_pos" 4
.IX Item "peek_pos"
.IP "peek_move" 4
.IX Item "peek_move"
.IP "move" 4
.IX Item "move"
.IP "undo" 4
.IX Item "undo"
.PD
.SH "METHODS"
.IX Header "METHODS"
.IP "_init [@list]" 4
.IX Item "_init [@list]"
\&\fIInternal method.\fR
.Sp
Initialize an AlphaBeta object.
.IP "ply [$value]" 4
.IX Item "ply [$value]"
Return current default search depth and, if invoked with an
argument, set to new value.
.IP "abmove [$ply]" 4
.IX Item "abmove [$ply]"
Perform the best move found after an AlphaBeta game-tree search
to depth \f(CW$ply\fR. If \f(CW$ply\fR is not specified, the default depth is
used (see \f(CW\*(C`ply()\*(C'\fR). The best move found is performed and a
reference to the resulting position is returned on success, and
undef is returned on failure.
.Sp
Note that this function can take a long time if \f(CW$ply\fR is high,
particularly if the game in question has many possible moves at
each position.
.Sp
If \f(CW\*(C`debug()\*(C'\fR is set, some basic debugging is printed as the
search progresses.
.ie n .IP "_alphabeta $pos\fR \f(CW$alpha\fR \f(CW$beta\fR \f(CW$ply" 4
.el .IP "_alphabeta \f(CW$pos\fR \f(CW$alpha\fR \f(CW$beta\fR \f(CW$ply\fR" 4
.IX Item "_alphabeta $pos $alpha $beta $ply"
\&\fIInternal method.\fR
.SH "BUGS"
.IX Header "BUGS"
The valid range of values \f(CW\*(C`evaluate()\*(C'\fR can return is hardcoded to
\&\-99_999 \- +99_999 at the moment. Probably should provide methods
to get/set these.
.SH "TODO"
.IX Header "TODO"
Implement the missing iterative deepening alphabeta routine. 
.SH "SEE ALSO"
.IX Header "SEE ALSO"
The author's website, describing this and other projects:
<http://brautaset.org/projects/>
.SH "AUTHOR"
.IX Header "AUTHOR"
Stig Brautaset, <stig@brautaset.org>
.SH "COPYRIGHT AND LICENCE"
.IX Header "COPYRIGHT AND LICENCE"
Copyright (C) 2004 by Stig Brautaset
.PP
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself, either Perl version 5.8.3 or,
at your option, any later version of Perl 5 you may have available.