Author: José Carlos
Date: 14:13:41 04/25/02
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On April 25, 2002 at 15:27:26, Robert Hyatt wrote: >On April 25, 2002 at 13:49:42, Dann Corbit wrote: > >>On April 25, 2002 at 13:26:43, Robert Hyatt wrote: >> >>>On April 25, 2002 at 12:39:36, J. Wesley Cleveland wrote: >>> >>>>On April 25, 2002 at 02:54:03, Andreas Herrmann wrote: >>>> >>>>>Hi, >>>>> >>>>>I want to implement double nullmove in my chess engine again. Now i'm searching >>>>>for Zugzwang postions, which should be solved by double nullmove instead of >>>>>normal nullmove. >>>>>Another question: How much time costs the double null move in the average. >>>>>I have tested it in some positions, and my engine needs about 30 to 40 percent >>>>>more time for the same search depth. Is that normal or is that to much. >>>> >>>>That seems like far too much. Are you reducing the search depth again for the >>>>second nullmove and only doing it when the first nullmove causes a cutoff? You >>>>might also not want to do it too near the leafs, i.e. if the first nullmove goes >>>>directly into your quiescence search. >>> >>> >>>One simple test... determine how often, in normal positions, the _second_ null- >>>move search fails high. Whenever it does, the the first null-move search fails >>>low and is useless. that is probably where the cost is being exposed... >>> >>>In zug positions, the second fail high will cause the first to fail low, which >>>prevents zug problems. But if it also causes a large number of normal positions >>>to fail this test as well, then it is losing part of the advantage of null-move >>>in general... >> >>I had a notion about double null move -- >> >>Implement double null move in the place where normally you will just turn null >>move off [except for check]. Use your regular null move algorithm as always, >>but when conditions indicate null move is not a good idea, switch to double null >>move. > > >If it was easy to identify positions where a null-move might cause problems, >the problem would already be solved. > >:) But I think Dann's idea is very logical, since a lot of us simply disable null move in some positions. Using double null move _only_ there must be better than disabling it. Of course, that doesn't solve the problem of zugzwang in unepected situations. José C.
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