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Subject: Re: Null-Move: Difference between R = 2 and R = 3 in action

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.


>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it could conclude less than a small outdated fullwidth search, so was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
>DIEP's probably only exception here, it needs a supercomputer to get
>that depth ;)
>>    Christophe

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