Author: Robert Hyatt
Date: 08:15:50 04/10/01
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On April 09, 2001 at 23:40:21, Jon Dart wrote: >>On April 09, 2001 at 17:04:09, Vincent Diepeveen wrote: > >> An interesting thing is lazy evaluation, as the problems of it are >> very similar to futility pruning. > >As another poster has said, it is not really risky to exit the eval early if >you're certain you are going to be have a score outside the search bounds. I >have a test mode where it goes through the full eval always but also checks to >see if it would have done a lazy exit, and if so, if it would have done so in >error. I run it once in a while and expect no errors. > >> A possible compromise i found in tests was to increase the margin. > >Yes. Crafty apparently uses a 1 pawn margin for futility pruning in the qsearch. >I tried this and didn't like the results. Mine is almost 2 pawns. I do this because a _single_ move should not produce _huge_ score swings. The futility pruning is based on the stand-pat score, which means that the current position is evaluated, and the only possible change will be from the piece being captured, or the positional score the single capture can produce. I tried several values and have had good luck with the current one. > >I also account for trade bonuses and other adjustments to the material score >that would be made as a result of the capture. So I'm pretty conservative, at >least in the qsearch (I do other somewhat riskier pruning in the main search). >I've been trying some alternative strategies lately but haven't found reason to >make major changes so far. > >> My big question was: what score to return for example if evaluation in this >> position is e and e+ 3.5 pawns <= alfa ? > >> Must one return alpha, estimated evaluation or evaluation+3.5 pawns, >> when talking about e+margin <= alfa (idem story for e-margin >= beta) ? > >I return the estimated evaluation. But I fail to see that it makes a lot of >difference. If it's below alpha, you're not going to propagate this evaluation >up the tree, anyway. > >--Jon
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