Author: Tony Werten
Date: 01:08:12 04/24/01
Go up one level in this thread
On April 23, 2001 at 13:37:19, Andrew Williams wrote: >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. You don't have to do that, since you made a call to evaluate in the start of qsearch. Your threshold only has to be the largest gain you got from 1 move. Tony > >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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