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

Author: Christophe Theron

Date: 23:44:17 07/13/02

Go up one level in this thread

On July 13, 2002 at 21:26:30, Omid David wrote:

>On July 13, 2002 at 11:52:36, Vincent Diepeveen wrote:
>>On July 13, 2002 at 11:09:19, Omid David wrote:
>>>On July 13, 2002 at 10:33:19, Vincent Diepeveen wrote:
>>>>On July 13, 2002 at 04:47:16, Omid David wrote:
>>>>>On July 13, 2002 at 02:39:38, Dann Corbit wrote:
>>>>>>On July 13, 2002 at 02:22:00, Omid David wrote:
>>>>>>>On July 13, 2002 at 02:07:17, Vincent Diepeveen wrote:
>>>>>>>>I still do not understand which positions you talk about which R=2
>>>>>>>>is finding and R=3 isn't.
>>>>>>>I read your other post, that's also my point: Although at fixed depth, R=2 is
>>>>>>>much better than R=3 (see also "adaptive null-move pruning" Heinz 1999), in
>>>>>>>practice R=3 performs about the same as R=2 since on many occasions it finds the
>>>>>>>correct move one ply later with lower search cost.
>>>>>>By the way, if you have not found Vincent's post on double null move you should
>>>>>>look it up.  It is a clear win for sure.
>>>>>Yes it's a nice idea. But the main null-move pruning deficiency is its tactical
>>>>>weakness due to horizon effect. Zugzwangs are not a major problem, and as
>>>>>Vincent points out, he invented the double null-move idea just to show that
>>>>>null-move pruning is OK. Now nobody doubts effectiveness of null-move pruning at
>>>>>all, the only discussion nowadays is the depth reduction value.
>>>>I'm missing any position where you have a problem though. Seems to me
>>>>your thing is incredible weak, and or doing other dubious things which
>>>>gets looked up in hashtable, after which it weakens your program.
>>>>In DIEP i don't have all these problems.
>>>>  - no dubious forward pruning
>>>>  - no futility
>>>>  - no razoring or any of these techniques.
>>>>  - checks in qsearch
>>>>Just PVS with nullmove R=3 and a bunch of extensions. That's it.
>>>>Means that after a nullmove i don't get transpositions to positions
>>>>where you have stored a score which is based upon a dubious score.
>>>>Best regards,
>>>Why do you think there is a problem?! All the results I got are natural. I'm
>>>sure even in DIEP, R=2 works better under "fixed theoretical" conditions.
>>No it works worse, because i search at least a ply less deeply. If i search
>>a ply deeper that doesn't only mean i get a ply more. Because the depth
>>is already pretty decent it also means all extensions might get triggered
>>a ply extra (like singular extensions).
>>>However in practice you don't search to fixed depth and thus R=3 might be better
>>>in practice.
>>>My only point is that "R=3 might be better than most people consider it." (Take
>>>DIEP as a successful use of R=3)
>>>Have you published anything regarding double null-move?
>>I simply posted in CCC and RGCC. the thing is real easy.
>>allow 2 nullmoves in a row always, but not 3.
>>Exception is if both sides only have pawns (of course you
>>can solve a few testset positions sooner by saying that
>>if either side has only pawns you don't allow nullmove
>>FOR BOTH SIDES, but that's in reality not so smart to do).
>>Apart from that the normal conditions that i don't nullmove
>>when in check.
>>This in fact results in nullmove not missing zugzwangs anymore.
>>Of course for more than 1 zugzwang the extra depth needed is
>>pretty big.
>>Best regards,
>I'd rather see such articles as "double null-move pruning" in ICCA than the
>usual pure-theoretical-non-practical articles!

Double null-move sounds elegant, but actually it's a zugzwang detection search
at depth D-2R-2 (D=remaining depth, and R is the classic null move reduction

It is less flexible than a zugzwang detection search because:
1) the depth is fixed to D-2R-2, so you can't adjust it to a better value (and
D-2R-2 is not an optimal value).
2) it's less easy to declare the conditions determining when you want to do (or
avoid to do) the zugzwang detection (but this can be discussed).


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