Author: Vincent Diepeveen
Date: 08:54:44 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 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. For most of the positions in bs2830 diep needs a bigger plydepth then to find the solution then. Because if a tree gets researched somehow as it gives a cutoff the ply below, then in hashtable i have score <= estimated evaluation, which will render a cutoff for me next time, whereas in reality it might be alfa-very_little Or in real bad luck cases alfa+something :) >--Jon
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