Author: Christophe Theron
Date: 10:18:40 07/17/02
Go up one level in this thread
On July 16, 2002 at 11:01:23, Vincent Diepeveen wrote: >On July 15, 2002 at 13:11:09, Christophe Theron wrote: > >>On July 15, 2002 at 08:37:34, Omid David wrote: >> >>>I don't think using double null-move is a good idea in practice, since in >>>midgame the chance of zugzwang is negligible and thus it's superfluous (I doubt >>>if even DIEP uses it). However the contribution of double null-move is that it >>>gives legitimacy to the null-move pruning idea, proving that it _is_ a correct >>>search method (anyway, no one doubts null-move nowadays). >> >> >> >>Why does double null move prove that null move is a correct search method???? >> >>Doing two null moves in a row means going back to standard search (a search not >>involving an illegal move like null move is). >> >>I fail to see how it legitimates null move. > >Double nullmove legitimates (duh can't you use easier to spell words) >itself, for the obvious reason that it is provable now that a search >depth of n ply, where i may pick n, is going to solve any problem you >give it. OK, I see now. However, it is not true. Due to a nasty interaction with the hash table algorithms, just allowing 2 null moves in a row will NOT solve any problem. It is necessary, in order to solve any problem, to add some logic in the HT algorithms, or to disable the HT completely. Christophe >Normal nullmove, if you remember the discussions a few years ago, >especially around 98 and 99, it was told to be an inferior way of >search, because for *any* selfpicked depth n for the nullmove search >it could conclude less than a small outdated fullwidth search, so was >the theory. > >This is not true of course. > >Reality is that only a few problems need a bit bigger search depth >with double nullmove, and most are far endgames. > >In middlegame it's very seldom one needs 3 ply more than a fullwidth >search would get. > >Note that getting a fullwidth search of more than 12 ply is impossible >whereas most get 14-15 ply with nullmove nowadays easily in tournament >practice. > >DIEP's probably only exception here, it needs a supercomputer to get >that depth ;) > > > > >> >> >> Christophe
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