[computer-go] tactical search in Many Faces

[Mark Boon]

On 28-sep-06, at 13:51, David Fotland wrote:

> I read each string with fewer than 4 liberties several times, to  
> distinguish between four possible states.  All of these searches  
> are done during evaluation, before finding eyes, groups,  
> life.death, and territory.
>
> 1) String is dead.  Prey moves first, prey wins all kos, hunter  
> answers all threats to adjacent strings, and prey is still  
> captured.  These strings can be eyes or connections for the attacker.
>
> 2) String is safe.  hunter moves first, hunter wins all kos, prey  
> answers all threats to adjacent strings, and prey can still make 4  
> liberties or 2 eyes always.  These strings can be part of living  
> groups.
>
> 3) String is threatened.  String is not dead (from earlier  
> search).  Hunter moves first, prey wins all kos, hunter answers  
> threats to adjacent strings, and string is still captured.  These  
> strings can be unconditionally captured when hunter goes first, so  
> they are half-eyes.
>
> 4) String safety is unclear.  The result is a ko, or the search was  
> too big to resolve one of the above choices.  This string might be  
> captured, so it might be part of an eye.
>
> I limit each search to 150 unforced nodes.  I track which board  
> locations affect each search, so the evaluation doesn't repeat  
> unnecessary searches.  I have pretty good move ordering, so the  
> search is a simple alpha-beta without iterative deepening, but with  
> a transposition table.  An unforced node is a position where the  
> move generator gives more than one move.  In a ladder, the move  
> generator usually only generates one move at each ply, so a ladder  
> of any length counts as zero unforced nodes.
>
> David
>
>

David,

"hunter answers all threats to adjacent strings"

sounds like you'll never sacrifice stones, which I'm sure can't be  
the case.

Mark

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