[computer-go] Adjacency Vectors for Eyespace

[Peter Drake <drake@xxxxxxxxxx>]

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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