Author: Robert Hyatt
Date: 22:12:02 12/23/98
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On December 23, 1998 at 19:57:54, Roberto Waldteufel wrote: > >On December 23, 1998 at 19:27:34, Inmann Werner wrote: > >>On December 23, 1998 at 19:12:16, KarinsDad wrote: >> >>>Hi all, >>> >>>I understand the basic concepts of a null move search, however, what I do not >>>quite understand is when in a chess program would it be used. Would you use it >>>just after non-quiescent searches, specific cases of nq searches (e.g. checks or >>>piece takes), or in other areas of the tree? >>> >>>Do you use it just to find bad moves or is there a way to find good moves with >>>it as well? >>> >>>And when you use it, how extensively do you search with it? >>> >>>Thanks in advance, >>> >>>KarinsDad >> >>I use Null move only in the "normal" alpha-beta (not in q-search) >>I do it in each (nearly each) position before trying any other move. After doing >>the null move I call normal alpha beta, but with less depth. There again can >>occur Nullmoves, but never allow 2 in a row. When I get back my value, and it is >>>= beta I stop this tree and return beta without trying any move. This reduces >>the tree a lot. (But is not a really sure thing, but wrking fine.) >>Second, if the value is rather deep (nearly mate) I extend the search with one >>ply, cause there anywhere is a mate threat possible. Works also fine. >> >>Dont forget: Beware of Zugzwang!! >> >>Wish a happy Christmas >> >>Werner > >Hi Werner, > >Most of what you describe is the same as what I do, but I am interested to read >that you allow multiple null moves in the same line. I only allow one null move >in a line, which I implement by setting a flag after a null move that prohibits >further null moves in all descendant nodes. Have you compared the two methods >and found multiple null moves faster? Are null move related errors noticeably >more or less frequent with multiple null moves? > >Also, can you explain exactly how you use the null move score to trigger an >extension? Do you mean that you do this if the null move score is close to >"giving mate" or when it is close to "being mated" for the side to move? > >And zugzwang, the great danger for null move. I dissallow null moves when either >side has less than 3 pieces (not pawns). How do you do it? > >Merry Christmas, >Roberto "recursive null-move" means to allow more than one in a line... although there is little use in doing two in a row since both can't fail high. But yes, if you allow more than one you will see significant savings...
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