Author: Tony Werten
Date: 22:33:53 04/29/04
Go up one level in this thread
On April 29, 2004 at 23:19:54, Robert Hyatt wrote: >On April 29, 2004 at 17:06:29, Gerd Isenberg wrote: > >>On April 29, 2004 at 16:03:08, Robert Hyatt wrote: >> >>>On April 29, 2004 at 02:08:40, Tony Werten wrote: >>> >>>>On April 28, 2004 at 16:14:39, Gerd Isenberg wrote: >>>> >>>>>On April 28, 2004 at 13:45:05, Ed Schröder wrote: >>>>> >>>>><snip> >>>>> >>>>>>What is double nullmove? I only know recursive nullmove allowing multiple >>>>>>nullmoves. I also read about "allowing 2 nullmoves in a row". What are the >>>>>>differences? >>>>>> >>>>>>I use recursive nullmove, not allowing the next ply after the nullmove to >>>>>>nullmove. So: >>>>>> >>>>>> e2-e4 >>>>>> e7-e5 >>>>>> **-** // nullmove >>>>>> d7-d5 // do no allow nullmove >>>>>> >>>>>>When I remove that check I get a few percent speedup, results look okay. >>>>>> >>>>>>Ed >>>>> >>>>> >>>>>Hi Ed, >>>>> >>>>>yes Double Nullmove, suggested and invented by Vincent, allows to play two >>>>>nullmoves in a row, to efficiently get rid of zugzwang problems. It is recursive >>>>>too, and if i understand correctly, it works fine without any nullmove >>>>>precondition: >>>>> >>>>> if (!inCheck) >>>>> { >>>>> if ( move2thisNode != null || move2ParentNode != null ) ( >>>>> val = -doNullMoveSearch(depth-1-R,...); >>>>> if ( val >= beta ) return val; // return beta; >>>>> } >>>>> } >>>>> >>>>>May be Vincent may correct me. >>>>>It seems that there is an implicit kind of IID with 2R-2 too. >>>> >>>>Correct. Chech your hashtable again after the nullmove, if you didn't have a >>>>best move before. >>>> >>>>Then throw out IID. >>>> >>>>Tony >>> >>>I don't see how/why one would throw out IID. >>> >> >>Yes but with double nullmove you may search a line like that, eg. for a 12ply >>search: >> >>null null e4 e5 Nf3 Nc6 Bb5 a6 .... >> >>which is IMHO a kind of IID with depth-6, so if you store hash after null null >>with best found e4, and probe after after nullmove, it is likely to get a hit. >>Or? >> > >Several problems. > >1. Suppose the best move is a repetition. If you do a repetition check after a >double null move, you get an instant draw score very time. Useless. So you >have to turn it off. Now you don't realize that the move draws, so it won't be >best. Etc. Easily fixed. Just start checking for repetition 2 plies higher in case of a double nm. > >2. double null rips 8 plies from the depth. That will often collapse you into >the q-search where all you can play are captures. Captures are not the best >move far more often than they are. I nm, you nm. My turn. If a capture makes your nm fail low, it is the best move. If it didn't then your nm fails high which basicly means the current node is a fail low node, so no IID needed. Tony > >> >>>NULL can collapse search to q-search, which means the best you can hope for is a >>>capture should you search this position later. That's not the same as a "good" >>>move when depth>0. If you mean after the second null, you are now 8 plies short >>>of a full search, which in most middlegame positions is going to be into the >>>capture only search... >>>
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