Re: [computer-go] Adjacency Vectors for Eyespace

["William M. Shubert" <wms@xxxxxxxxxx>]

Something I knew. :-)

If you download the 10 year old cgoban 1 program, you will see that I
use something similar to find seki at the end of the game. It works
great! I still use it to this day in KGS and the CGoban 2 program.

Mine is a little bit more complex though, because I also have to deal
with dead stones in the eyespace...some shapes are potentially two eyes
(and thus not seki) when they are truly empty, but are always one eye
(and thus seki) when there are dead stones at the proper locations. For
example, three in a row with an empty space in the middle is
(potentially) two eyes, but three in a row with a dead stone in the
middle can always be kept to one eye by the opponent.

On Thu, 2005-07-28 at 21:43 -0700, Peter Drake wrote:
> Is the following a clever new idea, or something everyone already knew?
> 
> The shape of a group's eyespace (in the simple case where it's  
> completely enclosed and there are no enemy stones) can be mapped onto  
> an "adjacency vector" of five numbers.  This is a many-to-one  
> mapping, described below.  It is interesting because all shapes with  
> the same adjacency vector have the same life status (alive, dead, or  
> unsettled), as long as the edge/corner of the board is not involved.
> 
> Given a region, the adjacency vector is the number of points in that  
> region with 0, 1, 2, 3, and 4 neighbors.  For example, the adjacency  
> vector for four in a row is 02200.  The adjacency vector for the  
> "rabbity" or "flower" six (the only dead six shape) is 02310.
> 
> For unsettled groups, the killing move is always on a point with the  
> highest adjacency.  For example, in the "bulky" or "radial" five  
> (01310), the vital point is the one with three neighbors.
> 
> This might also be useful for non-contiguous regions.  For example, a  
> (fully-connected) group with eyespace 20000 is alive.
> 
> Peter Drake
> Assistant Professor of Computer Science
> Lewis & Clark College
> http://www.lclark.edu/~drake/
> 
> 
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