Re: [gnugo-devel] Semeai reading

[Gunnar Farnebäck]

I wrote:
> 1. Tactical reading mistake of a three liberty string causes an
>    overamalgamation which the semeai reading can't recover from.
>    STS-RV_1:23
>
>    9 O O O . . .
>    8 X X O . . .
>    7 . X O O . .
>    6 X X X O . .
>    5 . . X O . .
>    4 O O O X X .
>    3 . O . X . X
>    2 O O . X X X
>    1 X X X X . X
>      A B C D E F
>
>    A8 is considered tactically dead.

This can be solved by further restricting the CC505 (conn.db) pattern
to not amalgamate over three liberty strings. This causes no breakage
on the regression tests and a minor 0.2% increase of owl nodes. Five
STS-RV tests are solved.

I'm somewhat suspicious about this change, however. Can someone see a
situation where it's likely to cause trouble?

> 2. The same thing but for a two liberty string. STS-RV_1:58
>
>       A B C D E F G H
>    19 O . X X O X . X
>    18 O . X O O X X X
>    17 O O O O O X . X
>    16 X X X O X X X X
>    15 X O X X O O O O
>    14 . O O X O . O .
>    13 X . X X O O O X
>    12 X X X O . O . X
>    11 O O O O O O . X
>
>    A19 is considered tactically dead.

Not amalgamating over two liberty strings seems rather excessive. The
patch
http://trac.gnugo.org/gnugo/attachment/ticket/199/gunnar_7_12.7c.diff
detects this particular situation where a nakade effectively changes
the two liberty string into a three or four liberty tactical reading.

See http://trac.gnugo.org/gnugo/attachment/ticket/199 for more details
and other attempts to improve the semeai reading.

/Gunnar