2.2 Group Determination
Stones and strings are catalogued into groups: any stones which are l00% connected are considered groups. A tactical search on all strings with less than 4 liberties is used to determine which strings are definitely dead. Dead strings are not included as part of any group.
2.3 Eye Identification
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Identifying eyes is achieved in a two step process: l. eye space is determined, and 2. individual eyes are identifled from the eye space. A floodfill type algorithm is used toidentify contiguous regions in which opponent connectivity probability is low. Points in those regions whose 8 neighbouring points are mostly clear of opponent connectivity probability are considered to be eye space.
Individual eyes with a groups eye space are identified by shape. There are several grades of eyes with the grade being a function of the opponent's connectivity map. Eyes with a grade above a certain level (see section 2.4) are considered to be true eyes.
2.4 Stone Safety
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The safety of each group is detemlined by the nultber of true eyes it has, The safety proccss is repeated 5 times; each successive pass is more pessimistic about which points will eventually becomc true eyes(i.e., the threshold is raised for selecting which grade of eyes will eventually become true eyes). The final safety value for a group is the average of its safety scores on each of the 5 passes.
2.5 Radiation Function
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The safety value for each stone is radiated to the nearby empty points in proportion to the connectivity probabi1ity map for that stone. The inverse of a stones safety (l00% - safety) is radiated in the same manner and contributes to the opponents radiated value i.e.,dead stones radiated full opponent safety.
Black and white radiation (including inverse radiation) is summed at each empty point.
2.6 Territory
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Black and white territory is estimated from the radiation values of the empty points.
The difference between black and white territory is returned as the evaluation of the hypothetical move for which it was generated.
