Author: David Eppstein
Date: 11:35:11 11/20/97
I thought I would share with the group a technique I tried yesterday, to get the program I'm working on to play better in a class of positions where it was having horizon-effect problems. I identified a class of "suspicious moves", moves that are a priori unlikely to be correct but that are reasonably likely to be used as delaying tactics in the horizon effect (and that were in fact occurring in the horizon effect problem positions I was looking at). The moves I classified as suspicious were non-captures when a seemingly good capture is available. The move ordering I use naturally places these moves later than the captures, as I think would be true in many or most programs. Anyway, if I search a suspicious move and it appears worse than previously searched moves at the same node (i.e. below alpha), I trust that result. But, if it comes in greater than alpha, I immediately become suspicious and search the same move to one greater ply. The deeper search result then becomes the value of that move. The intention is that this extension doesn't blow up the search tree size very much (because suspicious moves are rarely chosen as best) but improves the search accuracy. It is hard to be objective, but my program does seem to be playing better after this change. Is this technique common in other programs? Can anyone suggest refinements that would make it work better?
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