[gnugo-devel] OWL tuning: blocking escape with a knight's move

[Martin Holters]

I arend2:10, after two steps of reading (b G3 w F4), the situation looks
like this:

6|...O....
5|..O.X...
4|...X.O..
3|..OX.OX.
2|..OOXX..
1|........
 +-------.
  ABCDEFGH

Here, gnugo misses the nice move at H5, capturing the two white stones,
rejecting G3 in the first place. (G5 instead of H5 does not work, as
then white can force his way out with a series of ataris after w G4 b
H4, starting at H3.)

The patch below solves this, adding a suitable attack pattern. However,
it breaks strategy5:225 and ninestones:40. In the latter, the semeai
reading looks bogus with and without the patch and I have not really
figured out why the patch results in preferring D2 over C3.

In strategy5:225, the now proposed move L11 matches exactly the pattern
and indeed looks quite interesting, but IMHO does not work in this
situation (some better Go player please confirm), but gnugo misses the
correct defense in the reading process. If time allows, I will
investigate this further and might add a suitable defense pattern in the
coming days.

/Martin

diff --git a/patterns/owl_attackpats.db b/patterns/owl_attackpats.db
index ee75579..3db44e3 100644
--- a/patterns/owl_attackpats.db
+++ b/patterns/owl_attackpats.db
@@ -1853,6 +1853,26 @@ X.O
 :/,n,value(90)
 
 
+Pattern A426
+# See e.g. arend2:10
+
+?..?        
+*..O
+..Y?
+.O??
+
+:8,-,value(80)
+
+?ab?
+*..O
+CDe?
+fG??
+
+; lib(G) == 3 && lib(e) > 2 && xplay_defend(D,C,f,G)
+; && (owl_escape_value(a) > 0 || owl_escape_value(b) > 0 
+;     || owl_escape_value(C) > 0)
+
+
 #########################################################
 #                                                       #
 #          Eye reducing moves on the second line        #