I did a ladder reader once. Basically it's an alpha beta search where you focus on one group only, and that group has limited liberties. If it's strictly ladder reading, you only consider attacks that reduce the liberty count of a specific string to 1 (atari moves in other words) and defenses that bring up the count to 2. You stop the search when the liberty count can be increased to 3 or there are no moves that fit your criteria.
Another trickier class of moves to consider for defenses are captures of stones that are attacking the target group. That is more complicated than just moving to liberty points. There are many optimizations possible and I think many sophisticated programs also consider target chains that have more than 2 liberties and you can also prune based on patterns and so on. What I've given you is pretty much the limit of my knowledge of ladder reading but I know it can get a lot more sophisticated than what I describe depending on how you want to use it. - Don On Thu, 2008-07-31 at 15:50 -0700, 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? > > Peter Drake > http://www.lclark.edu/~drake/ > > > > _______________________________________________ > computer-go mailing list > [email protected] > http://www.computer-go.org/mailman/listinfo/computer-go/ _______________________________________________ computer-go mailing list [email protected] http://www.computer-go.org/mailman/listinfo/computer-go/
