Author: Roberto Waldteufel
Date: 16:57:54 12/23/98
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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
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