Author: Andrew Williams
Date: 13:25:37 12/29/03
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On December 29, 2003 at 09:27:54, Tord Romstad wrote: >On December 28, 2003 at 20:56:06, Tom Likens wrote: > >>I'll give it a shot. Essentially, what I've been experimenting with is >>aggressively reducing and/or pruning various branches of the tree depending >>on the current evaluation of the position and the previous level evaluation. >>If things don't seem to be improving (or getting worse) then I either... >> >>1) reduce the depth the branch is searched or >>2) eliminate it altogether. >> >>So far I've restricted this rather severely to positions where neither king >>is in check, no other extensions have been triggered, the last move played was >>not a null move, non-winning captures, non-hanging pieces etc. > >You may also find it effective to be conservative about pruning and reductions >at nodes where there has been an extension in one of the last three or four >plies of the path leading to the position. The disadvantage of doing this is, >of course, that the path-dependency of the search decisions becomes >even bigger. > >>One of the problems I've identified is that two identical positions may >>not be pruned/reduced in exactly the same way, if their parent scores differ. >>Storing the score for these nodes in the hash table is potential trouble, >>since transpositions may have different scores. >> >>Uri's idea of only using these nodes for move ordering may do the trick but >>I haven't really evaluated it yet. More than likely in the next day or two, >>I'll add some scaffolding to my code to catch these type of nodes and gather >>some statistics. Right now it's mostly guesswork. > >A technique I have found useful during development is the following: > >Instead of actually doing any forward pruning or reductions, set a local >variable >that says "I would have pruned this move if forward pruning was enabled". If it >turns out that the move fails high, print the position and the move to a log >file. >By studying the log file, you can identify cases which your pruning techniques >fail to understand, and use this information to improve the accuracy of your >pruning. > >Tord I do this a LOT. Andrew
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