Author: Uri Blass
Date: 09:02:23 12/20/02
Go up one level in this thread
On December 20, 2002 at 11:26:28, Richard Pijl wrote: >On December 20, 2002 at 10:54:01, Vincent Diepeveen wrote: > >>On December 20, 2002 at 08:23:59, Russell Reagan wrote: >> >>No futility is 100% different from lazy evaluation. >> >>Futility in fact selects less moves (in qsearch) >>based upon alfa or beta and lazy evaluation gives >>back a quick score a lot of the times. > >They are still related in a sense that both 'cut-off' the work to be done by >saying that it can't get good enough to improve alpha, so better stop working on >it. >> >>If you search a ply deeper a futile pruned move should not >>get pruned, whereas a lazy evaluated position will give problems >>no matter what depth you search. >> >>In contradiction to draughts where everything is seen fullwidth, >>in computerchess the effect of futility can be very bad too, >>because last 3 to 4 plies (R=2 versus R=3) the qsearch is returning >>back a score instead of a full search. >> >>If that misses major problems then you are in trouble. >> >>The argumentation of Heinz that futility is correct, is using the >>assumption that an evaluation doesn't get a big score for positional >>matters. The problem is that todays top programs do give big scores >>though. > >Although Baron is not a top program yet I'm starting to feel this. >To be sure that the wrong nodes aren't getting pruned I wrote a little piece of >test code. It returned the highest difference it found between the lazyeval >score and the full eval score (but not with passers on the board, and not in the >endgame). I added 20% to this and that was the threshold used for both lazyeval >and futility pruning. It turned out that with every release of the Baron this >value increased. >Now I'm working on 0.99.4 and the margin was getting very large, more than 5 >pawns. I think that it may be interesting to see the position that you talk about When do you see a difference of more than 4 pawns between the static evaluation and the lazy evaluation? I can imagine positions when the positional score is more than 4 pawns but I think that in these positions there are easy ways to detect a suspect that something is wrong also in a fast evaluation. Uri
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