Author: Robert Hyatt
Date: 21:44:42 08/26/05
Go up one level in this thread
On August 27, 2005 at 00:28:59, rasjid chan wrote: >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 That will take some thought. I don't personally like the idea of doing one thing to PV nodes and something else to non-PV nodes. That means that all moves but the first are searches more recklessly, making it harder to find a sudden killer-type move after searching the first move...
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