Author: Ulrich Tuerke
Date: 08:13:15 04/23/01
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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. Greetings, Uli > >Regards, >Dieter
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