On Tue, Jan 22, 2008 at 09:51:11PM +0100, Alain Baeckeroot wrote:
>
> Le mardi 22 janvier 2008, Michael Williams a écrit :
> > > ... perhaps only uniformly random playouts
> > > will scale to perfection.
> >
> > The reason that MC/UCT scales to perfection is because of the UCT part,
> > not the MC (playout) part. People seems to forget this a lot.
> >
> I agree on this _only_ if the UCT check all possible moves.
> If not one can be limited by the quality of the playout.
I think we may be confusing two different things here:
a) Using all "possible" moves in the playouts to evaluate a leaf in
the UCT tree
b) Making the UCT search all "possible" moves in a position
These two are related, and I suspect often people use the same code for
listing the "possible" moves, so they tend to be the same in many programs.
Theoretically speaking, errors and bias in those two may well result in
different things.
Most MC implementations (that I know of) avoid playing in one-point eyes.
That is alrady a deviation from "all legal moves", but one that makes
perfectly good sense. Yet there is at least one exception, where playing into
an one-point eye can create a nakade, and kill a surrounding group...
The selection of "possible" moves for a node in the UCT tree can be somewhat
slower, since it is not done nearly as often. Also, adding bad moves here
costs less than in the MC playout, since the UCT algorithm can see that they
will not lead anywhere, and not give them so much attention.
I don't (yet?) have an UCT program, so I can not test this. Some day when I
have one, I will try to see how much it will help or hurt to try all legal
moves in the UCT portion... If someone else tries it before, let us all know!
- Heikki
--
Heikki Levanto "In Murphy We Turst" heikki (at) lsd (dot) dk
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