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Subject: Re: When to do a null move search - an experiment

Author: Gerd Isenberg

Date: 22:29:30 04/27/04

Go up one level in this thread

On April 28, 2004 at 01:11:23, Gerd Isenberg wrote:

>On April 27, 2004 at 21:54:49, Uri Blass wrote:
>>On April 27, 2004 at 21:00:22, Vincent Diepeveen wrote:
>>>On April 27, 2004 at 11:43:36, José Carlos wrote:
>>>>On April 27, 2004 at 08:37:34, Tony Werten wrote:
>>>>>On April 27, 2004 at 03:33:26, Bas Hamstra wrote:
>>>>>>About double nullmove: I tested this in some pawnendgames to see if it could
>>>>>>handle zuzwang problems, but I don't see it perform any better than normal
>>>>>>nullmove. Can Vincent or you post a position where double null outperforms
>>>>>>normal null? I agree the idea is elegant, but I just don't see it work.
>>>>>I switch it off in pawns only endgames. Couldn't figure out why it wasn't doing
>>>>>as well as it sounded.
>>>>  I can't think about it now, but I recall this thread where an interesting
>>>>discussion about double null move came up:
>>>>  José C.
>>>Christophe wrote that down just to let you guys believe you should search
>>>Practical chances of it happening is small, not zero but very close to it.
>>>Additionally you can add a single 'if then else' condition in transposition
>>>table cutoff to avoid the theoretical scenario that christophe describes.
>>>Look the alternative to double nullmove is doing something dead slow like what
>>>Gerd is doing, or what i used to do in my draughtsprogram; a verification
>>>search, which is just a fullwidth search of n-R ply. So not the later posted in
>>>ICGA verification search. Verification search already was excisting in other
>>>publications than in the ICGA. So Omid just stole the name kind of for something
>>>working crappy :)
>>Omid did not steal the idea.
>>You simply did not understand Omid's ideas.
>>Omid's idea is not mainly to detect zugzwangs but to detect tactics earlier.
>>Null move pruning means that there are tactics that you need more plies to see
>>because of the horizon effect when you cannot detect the threat.
>>With verified null move pruning you can see it 1 or 2 plies earlier.
>>Doing checks in the qsearch cannot solve the problem because there is tactics
>>that is not based on checks.
>>>Basically all those approaches eat shitload of nodes to say it *very* polite.
>>Basically I see no reason that verification search to detect zugzwangs needs to
>>eat many nodes(Omid's idea is not verification search) and common sense tells me
>>that if the depth is reduced enough it does not eat many nodes.

oups, sorry for the empty reply...

I tried double nullmove suggested by Vincent too, without any precondition like
eval - margin >= beta. Vincent is probably right - it seems to work great, and
solves a lot of test positions a few percent faster. But with some positions,
specially with fail-high or -low behaviour the solution needs more than the
double time than single nullmove in a row with verification search in my
program. Two examples from BT-test:

2bq3k/2p4p/p2p4/7P/1nBPPQP1/r1p5/8/1K1R2R1 b - - ; bm c8e6
k7/8/PP1b2P1/K2Pn2P/4R3/8/6np/8 w - - ;bm e4e1


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