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Re: [gnugo-devel] Extremely bad mistake


From: SP LEE
Subject: Re: [gnugo-devel] Extremely bad mistake
Date: Thu, 12 Jun 2003 21:12:24 -0700




SP Lee wrote:
> Yes, I'm still learning the basics of the code, but I'm sure the
> suicide reading is wrong in this case. I have made the variable
> verbose=3.

Ah, that might explain things. Could it be that you have been fooled
by the very incomplete RTRACE messages? I was thinking those were
merely useless but maybe they should be considered directly harmful.

Would anybody mind if I just remove them? (Historically these may have
been useful in the early development of the tactical reading but have
been superseded by more advanced techniques and have not been
maintained.)

> What I have traced is, from the moment gnugo was "considering attack
> of C19", until gnugo checked A16 in is_suicide in board.c, where I
> found board[41]=0 (A18 is empty). Of course, board[41] was 1 in the
> early analysis stage, but I don't know yet when it was changed to 0.
> Maybe somewhere it's not propagated through to the defense checking.
> The tracing message showed " A16 would be suicide".

No, this doesn't sound right. It would be too fundamental to have
passed unnoticed. I would rather suspect that the traces are
misleading.

/Gunnar



Hi Gunnar,

I was indeed misled by the tracing messages. It was not started by attacking C19 at A18 and A16 was at that moment indeed suicidal. Sorry for my misleading message.

Now I have found the right sequence of what GNUGO thought. It is A18, A16, A17. After this the group C19 (and A19) has again 2 liberties and is in turn to make a defensive move. However, the reading process seems not to be aware of the PASS move (tenuki) and by filling any of the liberty, the group C19 was announced 'dead'. Yet the only choice at this moment is tenuki.

I had tried to add some code to do the PASS move, but I was not succeeded. Do you have a good solution?

SP Lee

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