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In GNU Go 2.6 extensive use was made of an algorithm from Bruno Bouzy's dissertation, which is available at: ftp://www.joy.ne.jp/welcome/igs/Go/computer/bbthese.ps.Z This algorithm starts with the characteristic function of the live groups on the board and performs `n' operations called dilations, then `m' operations called erosions. If n=5 and m=21 this is called the 5/21 algorithm.
The Bouzy 5/21 algorithm is interesting in that it corresponds
reasonably well to the human concept of territory. This
algorithm is still used in GNU Go 3.6 in the function
estimate_score
. Thus we associate the 5/21 algorithm
with the word territory. Similarly we use words
moyo and area in reference to the 5/10
and 4/0 algorithms, respectively.
The principle defect of the algorithm is that it is not tunable. The current method of estimating moyos and territory is in influence.c (see Influence). The territory, moyo and area concepts have been reimplemented using the influence code.
The Bouzy algorithm is briefly reimplemented in the file scoring.c and is used by GNU Go 3.6 in estimating the score.
Not all features of the old moyo.c from GNU Go 2.6 were reimplemented—particularly the deltas were not—but the reimplementation may be more readable.