Author: Bas Hamstra
Date: 14:53:23 12/04/02
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On December 04, 2002 at 12:36:44, Jon Dart wrote: >On December 04, 2002 at 03:43:09, Bas Hamstra wrote: > >>It is not the same IMO. I think Jon means this: suppose Eval is below alpha. >>Then in Crafty you calculate Delta=Alpha-Mat-Margin. However more accurate might >>be Delta=Eval-Margin. IE you prune based on Eval rather than material. >>I tried this, and the result is it will throw out less captures while I see no >>noticable improvement in accurracy. > >Yes, this is what I meant. Note that if you do an early exit from the scoring >function (lazy eval) then you need to adjust that if using this technique. E.g. >if you stop when you know the score is below alpha, that's wrong now, because >the amount the score is below alpha matters (cutting off early if you are above >beta is not a problem). > >--Jon I must confess I never have realized this, I will try it again, it might matter. But at the moment (actually the last years) I don't do futility at all, only straight SEE<0 pruning. IMO futility in the qsearch is only a (small) win if you have a Crafty-like mini-qsearch, otherwise it is useless. I does not combine well with a qsearch in which you do not evaluate a position when InCheck. At least according to my experience. I take the small penalty of leaving it to the lazy eval in the next ply, which is much more accurate. Bas.
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