Author: rasjid chan
Date: 21:28:59 08/26/05
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On August 26, 2005 at 15:38:06, Robert Hyatt wrote: >On August 26, 2005 at 15:27:51, Alvaro Jose Povoa Cardoso wrote: > >>>My first thought is that the number of "fail lows" is irrelevant. What you >>>really want to avoid is a reduction on a move that might fail high. Any move >>>will fail low in some situations, but you want to handle the "typical" case >>>correctly and not reduce if there is a reasonable chance the reduction will hide >>>something. >> >>So, you are saying history based pruning is not a safe thing to do? >>Or are you saying I should use tipical history values instead of counters? >> >>Alvaro > >I don't know how safe it is. Bruce Moreland and I played with this idea back >around 1996 or so, but we were not paying any attention to the actual moves >themselves (for example, never reducing a checking move perhaps) so that what we >fooled around with never worked very well in actual games. >I'm not sure what I would use, should I try to play with this again. In fact, I >have it on my "to do list" since such ideas (futility) have been used in Crafty >with good results already, and this is just another variation on that sort of >theme... A related problem is when it is good to extend or reduce. In a past thread "why is fruit so strong?" many(including Fabien) only made general(good) comments and only Thomas of Toga was definite - "That's easy to answer..." and he mentioned :- Fruit only extends pv nodes and don't reduce pv nodes(I'm not sure if it is without exception). Reductions only done in non-pv nodes. I come to figure that there may be a point for this. All child nodes of pv-nodes usually have positions with one piece position differing. Static evaluations of these child nodes have higher average probability of being close to the pv score. Nodes far away from the pv have a high average probabilty of having scores away from the pv score. In any non-critical stage of a game, the pv scores from one iteration to the next do not change much and this means the set of pv node moves all have greater probability to be in the next pv and hence Thoma's observation. This may affect any pruning scheme so that a workable scheme may seem not to work. Rasjid
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