On Jul 31, 2008, at 4:24 PM, Mark Boon wrote:
On 31-jul-08, at 19:50, Peter Drake wrote:
I know we had this conversation recently, but I just can't seem to
get my head around writing a ladder reader. What, exactly, does the
ladder reader do?
Our approach was to read out ladders involving the last stone
played. In the playout (beyond the tree), if the attacker can
capture by continuing a ladder, the attacker plays that move. If
the defender can escape by running, the defender plays that move.
Otherwise, a random move is played.
The trouble seems to be that, once the attacker plays, there's
nothing more for the ladder reader to say. At this point, it's
50-50 whether the attacker or defender will play on the defender's
last liberty. Thus, the ladder reader doesn't give any pressure to
stop running when caught in a ladder.
What am I missing?
What you're missing (or so it seems to me) is that it's not to
prevent from running a ladder that is caught.
Really? My motivation has been to prevent my program from
embarrassingly running in just those situations. Is there something
other than a ladder reader used for this?
It is to ensure to escape when you can or capture when necessary to
prevent an escape. And not only the last stone played of course, it
could be the neighbour of the last stone played as well.
The neighbor point is useful. Of course, as Don pointed out in another
message, there are always additional complexities to add -- what if
one of the attacking groups is in atari, or can be put in atari?
I'm more interested in the bigger issue: exactly what question is the
ladder reader trying to answer? When does it suggest a move and when
doesn't it?
Peter Drake
http://www.lclark.edu/~drake/
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