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Re: [gnugo-devel] Olympiad games

From: Gunnar Farneback
Subject: Re: [gnugo-devel] Olympiad games
Date: Thu, 11 Jul 2002 18:02:05 +0200
User-agent: EMH/1.14.1 SEMI/1.14.3 (Ushinoya) FLIM/1.14.2 (Yagi-Nishiguchi) APEL/10.3 Emacs/20.7 (sparc-sun-solaris2.7) (with unibyte mode)

Arend wrote:
> I have seen similar problems, and I suggest starting at another end. C12
> looks worth owl attacking here, if it escapes, the surrounding groups will
> get weak. However, of course one shouldn't start doing this with B11 or B13
> (D11 looks acceptable in my opinion).

I agree that D11 would be an acceptable attack (of the single C12
stone that is, not when it was played in the game). But it isn't
really all that important whether it actually does kill the stone as
long as the outside is strengthened.

> I think it would make a lot of sense to do some serious effort on
> implementing a different move order for owl at stackp == 0. Further
> down the tree, we are only interested _whether_ we can kill/live. At
> stackp==0, where the move found by owl will often be the move
> played, it is very important to use the _right move_ to kill/live.

This is how the owl code always has worked, although not necessarily
very successfully. I think this is problematic and that it would be
better if the owl code always was allowed to return just any move
which is effective. Then the owl_does_attack() and owl_does_defend()
functions can be used to test potentially more attractive moves for
critical dragons.

> Hence, at stackp>0, the move ordering should be "most likely move to
> kill first", whereas at stackp==0 we want "the move that would be the
> best way to kill first".

I'd prefer to always have "most likely to successfully terminate
search quickly first". 

> I assume the different policy about vital moves (see comments in owl.c
> around 1285) according to stackp == 0 resp. stackp > 0 is motivated by
> the same reasoning.

Yes, it is.

> One way to go further than that would be to order the moves
> according to their territorial effect computed via the
> "dragons_unknown"-influence.

That's probably a good idea in any case.

> I am sure that at move 17, owl would find that D11 kills C12. This would
> be a perfectly fine move, punishing C12. So D11 should be tried first,
> and only if this does not kill, owl should try like B11.

D11 should be tried before B11 in that position regardless of stackp
== 0 or stackp > 0.

> G14 (57) probably has to be at G16, but may be hard to see without
> lookahead.

I assume you mean K14 (57) here. Is the intention of G16 to sacrifice
H15 in order to get D17 in return?

> B8 (69) looses a lot of points. The strategic (over-)valuation of B8
> is bogus, whereas Q16 is enormously undervalued here (is 16.5; 30 looks
> closer to the truth).

Q16 is occupied. Do you mean Q17? If so, with the plan to then block
at R16 or to let white live in the corner?

> Which looks correct; it does find the owl defense at S13 in the next
> move. Of course still better to play R12 in the first place, but S13
> would reduce the damage quite a lot.

I didn't find S13 sufficient to live (at least not without resorting
to semeai after a P14/O13 cut), but maybe I didn't read carefully

> O9 (119) is a bit strange. There is weird with the moyo size of
> L11 here.

O9 would have been a fine move if GNU Go had been clearly ahead. :-)

> The second game against Go4++ (game2-19-gnugo-go4-0-1.sgf) looks
> encouragingly close. If GNU Go would close its territory at move 80
> (or resits at H7 with move 86), it might be leading.

I imagine move 80 (or 82) could be fixed with some influence tuning.
Missing H7 looked like a serious mistake.

> However, this intruding into opponent's territory as
> black does with moves 83 and so on seems to be a strength of Go4++,

That's my impression too.

> so the victory was not undeserved. On the other hand, I am not sure
> Go4++ read this out, maybe it just tried, hoping that something good
> will happen.

It may well have read out correctly that G6 would bring something but
also wildly plays any move that seems likely to cause trouble

> (As it did even more so later in the game -- btw, were
> these games played with chinese rules, or will this be even worse at
> the century cup?)

Good question. It may very well be worse at century cup, but I think
GNU Go will be able to defend well against thrashing dragons, in
particular after my latest patch.

> J4 (144) is an annoying mistake caused by a huge shape bonus (shape+10).
> I often get the impression that such huge shape values cause a lot more
> trouble than they help to resolve. Maybe we should review all shape
> values bigger than +-6, or ignore the shape effect for moves with owl move
> reasons.

I wouldn't mind just eliminating all huge shape values and large fixed
values to see what happens. I think we have better tools to properly
solve the problems those patterns were intended for today than when
they were introduced, if we just can find them again. Quite a few of
them have probably been solved already by other fixes, in particular
the influence revisions, and the corresponding patterns only have the
effect to overcompensate now.


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