Author: Roberto Waldteufel
Date: 05:10:08 12/24/98
Go up one level in this thread
On December 24, 1998 at 01:12:02, Robert Hyatt wrote: >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... Hi Bob (and Werner) Thanks for the tip. I just tried this out, and early results seem to indicate a speedup af the order of 25% - quite a tidy saving! Sometimes I spend days on end trying to achieve a 4% or 5% speed-up somewhere, and this time I got 25% in about 45 minutes! :-) Merry Christmas, Roberto
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