Dave wrote: > We have seen a similar effect many times in MoGo. Often we try > something that seems like it should improve the quality of the > simulation player, but it makes the overall performance worse. It is > frustrating and surprising! Has anyone else encountered this?
I'm not surprised. The goal of Monte Carlo simulations should be to provide an unbiased estimate of the true min-max value with as low variance as possible. This has little to do with strength, unless you happen to find a perfect simulation player, but then the whole search business becomes moot. The fact that many modifications of uniformly random playouts simultaneously improve simulation playing strength and overall strength is a red herring. Uniformly random playouts are strongly biased to overestimate the value of having tightly connected stones since e.g. one space jumps become cut through disproportionally often compared to what happens in relevant paths through the min-max tree. Almost any change in simulation policy that counters this tendency will improve overall strength and likewise pretty much every sensible change will improve simulation strength compared to uniformly random play. At higher levels something that may happen is that a change in the simulation policy improves the skill at making life in tight spots, without changing other skills. This would likely improve simulation strength but would cause a bias for positions where there's room for a futile invasion that barely fails, decreasing overall strength. Similar phenomena have turned up in GNU Go over the years. If you tune tactical reading or life and death reading to find some new class of attacking moves, results are likely to become worse if you don't do matching changes in the capability to find defense moves. There's also the classical effect of fixing an obvious mistake just to find some regression tests starting to fail. Closer examination shows that the tests were previously only passing because there were two mistakes that cancelled each other and fixing one of them breaks the balance. /Gunnar _______________________________________________ computer-go mailing list computer-go@computer-go.org http://www.computer-go.org/mailman/listinfo/computer-go/
