Hello,
----- Message d'origine ----
De : Michael Williams <[EMAIL PROTECTED]>
À : computer-go <[email protected]>
Envoyé le : Mercredi, 23 Janvier 2008, 20h38mn 32s
Objet : Re: Re : [computer-go] Bent four in the corner was:Scalability problem
of play-out policies
ivan dubois wrote:
> I agree that the current implementation of Mogo (from what I know about
> it) will not know for sure that the D17 black group is 100% dead.
> It will think that it is X% dead and stick to that estimation, whatever
> thinking time you give it. X is a constant that does not depend of
> thinking time (no scalability).
>How are you arriving at this conclusion? It makes no sense to me.
Actually this is not true for this exact situation, but I think it is true if
the black group has enough external liberties.
Suppose it has 10 outside liberties, to make things very clear.
For the simplicity of my argument, suppose also that the big eye is almost
entirely filled with white stones (minus 1 liberty)
Here is my reasoning :
Starting from the root, there are some playouts where the black group dies,
and other where it lives. Let us note X the proportion of playouts that end
with the black group having been captured.
Now is there any move A, starting from the root, that will change this
ratio if you start the random playouts just after A ? I think clearly, the
answer is no, do you agree with that ? The only relevant possible move would be
to fill a liberty, but since all liberties will be filled anyway during the
playouts, this will not change anything to the scenario. The only thing that
matters is wether or not white plays first at the vital point every time the
eye is reduced during the playouts.
Using the same argument, there exists no sequence of less than 8 moves that
can change the value of X.
This means all these sequences of liberty filling will be considered to have
exactly the same value than playing a null move.
I think it implies that uct will "never" (of course in theory it will at some
point but I say it would require absurd computing time) find the sequence that
captures the group with 100% confidence, because this sequence begins with 8
apparently useless moves.
Ivan
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