> Just out of curiosity, what did you expect from the playouts? Nothing in particular, really; at this point I'm just trying to build up an intuition about what I can or cannot expect from them. At first, I thought light playouts would not fully explore, but at least randomly cover all possible games, so we wouldn't get good move sequences directly, but lots of useful statistics to work with; while heavy playouts would try to mimick more realistic games, so the statistics would be biased, but there'd be a better chance of getting good moves directly. That turned out to be somewhat naive on all counts, as the answers to my earlier messages showed!-)
There is no chance of covering all possible games, so uniformly random play (light playouts) definitely ignores some, and if realistic games are unlikely, and good move sequences even more so, then they get the least coverage. So, in the presence of limited resources, "no bias" is a bias on its own. And the way eyes and other rules knowledge are encoded for efficiency reasons introduces other biases as well. Heavy playouts never drop possible sequences, they just try to focus the available resources away from sequences that appear less promising. That can have unpredictable effects, so the "unpromising" sequences are kept in the pool, at low priority, and the resulting focussed playouts need heavy testing to get some measure of confidence in any improvements. In sum, there doesn't seem to be a good basis for understanding playouts and their optimisation, other than by trial and error. Those who've been through some cycles of trial-and-error probably have at least a vague intuition of what works and what doesn't (or didn't when they last tried), but there is depressingly little theory (and many of the references are infuriatingly vague - in the style of "there was a lot of discussion about that"; great! not! where, when, what keywords or references, please?-). I'm trying to build some of that intuition in advance, both to be able to focus my trial-and-error phase and to have some theory to complement the experiments. At the moment, the most puzzling aspect is that the uncertainties aren't bounded in any direction: the pseudo-eyes variations aren't subsets of each other (that can probably be fixed, and would result in a single best variation, at least for the three ones I've mentioned); the playout evaluation, while somewhat biased toward not seeing more complex properties of board positions, cannot even be said to give a lower bound on the score, because it will underestimate both the strength of positions and the strength of possible attacks against them (though knowing that much will be of some help at least). Currently, it seems as if even many of the tricks that seem to work wonderfully well don't really have a solid basis, so any tournament could throw up a game that puts the whole thing into doubt, by showing a hole in the test coverage big enough to drive a truck through (once pros and others know what to look for). Or not. But if a (very) occasional, weak player like myself can show up some of the biases in concrete board positions, then a real player, not to mention a professional, should be able to spot and exploit them in real games. Claus _______________________________________________ computer-go mailing list [email protected] http://www.computer-go.org/mailman/listinfo/computer-go/
