Re: [gnugo-devel] owl testcase

[Evan Berggren Daniel]

On Tue, 19 Aug 2003, SP LEE wrote:

>
> > Evan wrote:
> > > A simple owl testcase from a game today.
> >
> > A wonderful illustration why static eye analysis is so terribly
> > difficult. The position in the lower right corner is this:
> >
> > . . X . O . . . . 8
> > . O . X O . . . . 7
> > . O X X X O . . . 6
> > . O O X O O O O . 5
> > . . . X X O X . O 4
> > . O . X O O X . O 3
> > . . O O X X . X X 2
> > . . . . X . . . . 1
> > L M N O P Q R S T

...

> I have tried to simplify the problem as attached, on 9x9 board.
> Surprisingly, GG can solve the problem correctly. The situation is:
>
>    A B C D E F G H J
>  9 . . . . X . . . . 9
>  8 X X . X X O . . . 8
>  7 . . X O O O + . . 7
>  6 O O X . . . . . . 6
>  5 . . O O + . . . . 5
>  4 . . . . . . . . . 4
>  3 . . + . . . + . . 3
>  2 . . . . . . . . . 2
>  1 . . . . . . . . . 1
>    A B C D E F G H J
> While analyzing the problem "owl_attack A8", GG tried C9 and find a
> following answer directly at B9. While in the real game, GG answers R1
> with R2 during owl analysis due to pattern D1002. I have also tried to
> change the positions a little, but still can't repeat the flaw as in the
> real game. I hope someone with more knowledge of the static eye analysis
> and patterns can find the reason of this. Thus, why is the pattern D1002
> not matched on simplified board? And, why is the vital move not found in
> the real game?

There is a key difference here:

The stone at T3 in the game is not present at A7 in the simplified
position.  This changes the tactical analysis of the position, as the
defender has an extra liberty.  Gunnar pointed out that the external
connection (B7 on simplified board) is considered tactically unsafe in the
game position; the extra liberty should change that.

(I haven't actually checked this, but it should be correct)

Evan Daniel