Author: Andrew Williams
Date: 10:37:19 04/23/01
Go up one level in this thread
On April 23, 2001 at 11:13:15, Ulrich Tuerke wrote: >On April 23, 2001 at 10:58:27, Dieter Buerssner wrote: > >>On April 23, 2001 at 10:11:00, Ulrich Tuerke wrote: >> >>>On April 23, 2001 at 09:48:40, Dann Corbit wrote: >>[...] >>>> >>>>Just like NULL MOVE or any selective element for searching, it will cause some >>>>problems to be solved more slowly. However, I suspect it will cause *most* >>>>problems to be solved faster. That is the way it works with every good idea. >>> >>>Completely agreed. The above mentioned risk arises essentially if you have >>>chosen your cut threshold (too) close to alpha. >> >>There can also be some other "risks", depending on what the qsearch does. >>E.g. When you don't allow stand-pats, where the side to move is in check. >>When you cut such nodes, depending on material gain and alpha, you can miss such >>situations. >> >>I try to be careful to do the pruning in qsearch in certain situations. When you >>capture the last pawn of the opponent, you can reach a draw score. An example >>(similar to what we discussed recently). KNNP vs. K will have an high material >>advantage. If you grap the P, the material gain is much less than the gain in >>score. Also, when reaching pawn endgames, I try to be careful. > >Yes. I made similar experience. Quite generally, futility pruning in pawn >endings implies an unreasonable high risk. I think that this holds for the full >search as well as for the q-search. > >Neither do I cut when the colour to move is in check. > >> >>I think, this pruning idea saves less, than one could think. When you prune the >>node, all work, that would be needed for this node is a call to qsearch, and a >>call to eval (which will fail high). > >In comet, it does pay out. I observed that I win O(20%) by applying this kind of >q-search pruning, depending on the threshold chosen and position. > >> >>For the threshold, I use something based on largest positional advantage >>(dependant on the side). Of course, this won't give many cutoffs with Vincent's >>20 pawns :-) > >I use about a half pawn, which is perhaps a bit too aggressive. > Interesting. I use the highest positional score so far in the search, with a *minimum* of 2 pawns. At this point, I was about to talk about the conditions regarding pieces left that I use to control this... But I noticed that it includes the term (HOWMANYWHITEPIECES > 0), which is all very well, except that that macro includes the King in the count!! So this little discussion has identified a bug in my program :-) Thanks guys! Andrew >Greetings, Uli > >> >>Regards, >>Dieter
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