[Computer-go] another UCT bot

Dave Dyer ddyer at real-me.net
Wed Oct 26 22:56:37 PDT 2011

I've deployed a reasonably strong UCT bot at boardspace.net for
Fanorona (the "bestbot").

UCT worked really well in the opening phases of the game, but in endgame
positions (which are very positional) it tended to meander and eventually
draw, even in positions where it had an overwhelming numerical advantage
and an obvious (to humans) line of play.   

I tried various things to tweak it's endgame, including various hacks
to prune or shape the move tree;  and also (as an experiment) running
the search for an absurd amount of time.  None worked reliably.

It seems to be an intrinsic property of this game that end games give a
very weak "win" signal with random playouts.   I suspect this is also the
case with the opening phases of Go.   

The hack I eventually developed was to add a small top-level bias based 
on the static evaluator, which kicks the "all look the same" endgame 
moves in the right direction most of the time.  Since this is done
only once on root node, this has no impact on the overall speed.

The biggest problem with UCT in general is that there aren't
very many knobs to tweak - there's no obvious way to add knowledge
if you don't like the current results.

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