On Wed, May 15, 2013 at 12:37:26PM +0900, Hiroshi Yamashita wrote:
> >Many Faces reads ladders in both the tree and the play outs. In play-outs
>
> Aya reads ladders only in tree. In play-outs Aya checks killing
> two libs stones without search. So it can understand only easy
> cases up to 3 plies, but it was effective. I tried ladder in
> play-outs before, but I could not get good result.
In Pachi it's similar to Aya. We special-case only "ladders near the
edge of the board" which are trivial to read and are very helpful in the
playouts:
. O .
O X O
? . x?. ?
# # #
In the tree, I tried to be very smart about analyzing ladders without
playing moves on the board and with no backtracking etc., but too many
bugs kept appearing and that caused a lot of embarassment in Pachi's KGS
games. :) So I gave up and rewrote ladder check in a much more naive,
but reliable way and now Pachi has pretty much no problems with ladders
anymore.
But yes, in order to have MCTS deal with ladders correctly, a specific
heuristic is essential - correct ladder reading does not arise from
anything magic in the algorithm, unfortunately.
--
Petr "Pasky" Baudis
For every complex problem there is an answer that is clear,
simple, and wrong. -- H. L. Mencken
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