[computer-go] Scalability

["Persson, Magnus" <persson@xxxxxxxxxxxxxxxxxx>]

> -----Original Message-----
> From: Don Dailey [mailto:drd@xxxxxxxxxxxxxxxxx]

> But in each case, I got very chess-like improvements for increasing
> the number of nodes searched.  I did most of these runs on 9x9 boards
> but did one verify with a 19x19 board.  In short, any evaluation
seemed to
> scale.

I can confirm that go scales with increasing search depth with a complex
evaluation function as well.

I did some experiment this summer using my 19x19 evaluation function on
9x9 with traditional alfabeta search. I used 9x9 because the evaluation
function seemed to be fast enough in order to search up to ply 6
(playing games overnight). I tested different search depths against
gnugo 3.4 and there was some clear scaling with increasing search depth.
With my evaluation function there was a strong effect of odd/even search
depth. With odd depth the program would play unreasonable moves (because
it could always play some unreasonable attack as the last move). I did
some attempts at implementing quiescence search to the program with some
partial success. But Q-search is very hard to do in go (at least when
you only spend a few hours on writing the code). If one want to have a
very complex evaluation function as I do it might pay off to first think
about the "Q-search problem" when designing the evaluation function.
Since my evaluation function tries to accurately judge the stability of
groups statically then any move causing a position where a groups safety
is affected should be handled by a Q-search.

So at least in principle traditional chess techniques work in go but
since you only can search 2 ply with a complex evaluation function all
the cool chess stuff such as null moves and transposition tables has no
impact.

--
Magnus Persson
Center for Adaptive Behavior and Cognition
Tel: +49-(30)-82406-350
Cell phone: +49 163 6639868

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