[gnugo-devel] safety_3_10.1

[bump]

I've put up a patch called safety_3_10.1 at devel.html.

This patch implements a new test for when dragons are surrounded.
The idea is that this will be an ingredient in the computation of
the new weakness field. There is another way in which it can be
used, as I will explain later.

I believe it correlates pretty well with the intuitive sense of when a
group is becoming surrounded and may have difficulty living if it does
not already have two eyes.  The patch does not affect play but only
adds a command line option --decide-surrounded [pos] which allows you
to see the computation.

The idea is based on my imperfect recollection of and idea of 
Bruce Wilcox.

The convex hull of the neighbor dragons is computed, and a 
slightly larger area is also marked. If every friendly dragon
that meets the hull is contained within it, the dragon is
SURROUNDED. If every friendly dragon that meets the hull
is contained within the enlargement, it is WEAKLY SURROUNDED.
An examination of 9 test cases identified by myself and Arend
as ones where GNU is prone to neglect a weak dragon shows that in
every one of these cases the dragon is surrounded in this sense.

I also have the idea that one may be able to make use of
this idea to identify good defensive moves. This will involve
caching the polygon when a weak dragon is found. Then any
move matching an e or E pattern (as discussed in 
http://mail.gnu.org/pipermail/gnugo-devel/2002-October/003003.html)
is a good defense provided it lies outside the polygon.

If anyone wants to experiment with the patch, try running it
in a color xterm. More details about the 9 test cases are in
the patch comments.

Dan