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Subject: Re: Checks in the Qsearch

Author: Robert Hyatt

Date: 20:34:52 07/08/02

Go up one level in this thread


On July 08, 2002 at 15:00:46, Uri Blass wrote:

>On July 08, 2002 at 13:30:33, Robert Hyatt wrote:
>
>>On July 08, 2002 at 12:29:17, Uri Blass wrote:
>>
>>>On July 08, 2002 at 11:39:40, Robert Hyatt wrote:
>>>
>>>>On July 08, 2002 at 00:21:23, Christophe Theron wrote:
>>>>
>>>>>On July 07, 2002 at 23:53:16, Robert Hyatt wrote:
>>>>>
>>>>>>On July 07, 2002 at 23:42:03, Omid David wrote:
>>>>>>
>>>>>>>On July 07, 2002 at 21:43:47, Robert Hyatt wrote:
>>>>>>>
>>>>>>>>On July 07, 2002 at 16:47:33, Omid David wrote:
>>>>>>>>
>>>>>>>>>On July 07, 2002 at 16:36:57, Robert Hyatt wrote:
>>>>>>>>>
>>>>>>>>>>On July 07, 2002 at 11:48:27, Omid David wrote:
>>>>>>>>>>
>>>>>>>>>>>On July 06, 2002 at 23:23:28, Robert Hyatt wrote:
>>>>>>>>>>>
>>>>>>>>>>>>On July 06, 2002 at 22:29:44, Omid David wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>>On July 06, 2002 at 10:20:17, Robert Hyatt wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>>>On July 06, 2002 at 01:07:36, Ricardo Gibert wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>Okay, but so what?
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>So perhaps the idea of "forward pruning" is foreign to us as well...
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>I see no logical difference between deciding which moves are interesting and
>>>>>>>>>>>>>>>worth looking at and deciding which moves are not interesting and not worth
>>>>>>>>>>>>>>>looking at. It looks to me like 2 sides of the same coin, so your speculation
>>>>>>>>>>>>>>>that "perhaps the idea of "forward pruning" is foreign to us as well..." does
>>>>>>>>>>>>>>>not seem to be of any consequence.
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>However, that has been _the point_ of this entire thread:  Is DB's search
>>>>>>>>>>>>>>inferior because it does lots of extensions, but no forward pruning.  I
>>>>>>>>>>>>>>simply said "no, the two can be 100% equivalent".
>>>>>>>>>>>>>
>>>>>>>>>>>>>Just a quick point: The last winner of WCCC which *didn't* use forward pruning
>>>>>>>>>>>>>was Deep Thought in 1989. Since then, forward pruning programs won all WCCC
>>>>>>>>>>>>>championships...
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>In 1992 no "supercomputer" played.  In 1995 deep thought had bad luck and lost
>>>>>>>>>>>>a game it probably wouldn't have lost had it been replayed 20 times.   No
>>>>>>>>>>>>"supercomputer" (those are the programs that likely relied more on extensions
>>>>>>>>>>>>than on forward pruning due to the hardware horsepower they had) has played
>>>>>>>>>>>>since 1995...
>>>>>>>>>>>>
>>>>>>>>>>>>I'm not sure that means a lot, however.  IE I don't think that in 1995 fritz
>>>>>>>>>>>>was a wild forward pruner either unless you include null move.  Then you
>>>>>>>>>>>>would have to include a bunch of supercomputer programs including Cray Blitz
>>>>>>>>>>>>as almost all of us used null-move...
>>>>>>>>>>>
>>>>>>>>>>>I personally consider null-move pruning a form of forward pruning, at least with
>>>>>>>>>>>R > 1. I believe Cray Blitz used R = 1 at that time, right?
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>I believe that at that point (1989) everybody was using null-move with R=1.
>>>>>>>>>>It is certainly a form of forward pruning, by effect.
>>>>>>>>>
>>>>>>>>>Yes, and today most programs use at least R=2... The fact is that new ideas in
>>>>>>>>>null-move pruning didn't cause this change of attitude, just programmers
>>>>>>>>>accepted taking more risks!
>>>>>>>>
>>>>>>>>
>>>>>>>>I think it is more hardware related.  Murray Campbell mentioned R=2 in the
>>>>>>>>first null-move paper I ever read.  He tested with R=1, but mentioned that
>>>>>>>>R=2 "needs to be tested".  I think R=2 at 1980's speeds would absolutely
>>>>>>>>kill micros.  It might even kill some supercomputers.  Once the raw depth
>>>>>>>>with R=2 hits 11-12 plies minimum, the errors begin to disappear and it starts
>>>>>>>>to play reasonably.  But at 5-6-7 plies, forget about it.
>>>>>>>
>>>>>>>So using a fixed R=3 seems to be possible in near future with faster hardware,
>>>>>>>doesn't it?
>>>>>>
>>>>>>
>>>>>>Very possibly.  Or perhaps going from 2~3 as I do now to 3~4 or even 4~5 for
>>>>>>all I know...  I should say that going from 2 to 3 is not a huge change.  Bruce
>>>>>>and I ran a match a few years ago with him using Ferret vs Crafty with Ferret
>>>>>>using pure R=2, and then pure R=3.  We didn't notice any particular difference
>>>>>>at that time.  It played about the same, searched about the same depth, etc...
>>>>>
>>>>>
>>>>>Increasing R is pointless after 3.
>>>>>
>>>>>Because instead of having a null move search using 5% of your time (just an
>>>>>example, I do not know the exact value), it will use only 2% or 3%.
>>>>>
>>>>>The speed increase is ridiculous, and the risks are getting huge.
>>>>>
>>>>>The only thing you can get by increasing R after that is having a percentage of
>>>>>search spent in null move close to 0. So a potential of 2% or 3% increase in
>>>>>speed.
>>>>>
>>>>>And an big potential to overlook easy combinations everywhere in the tree.
>>>>>
>>>>>That's why I believe that working on R>3 is a waste of time.
>>>>>
>>>>>
>>>>>    Christophe
>>>>
>>>>
>>>>You are overlooking _the_ point here.  At present, doing 12-14 ply searches,
>>>>R>3 doesn't make a lot of difference.  But in the future, when doing (say)
>>>>18 ply searches, R=4 will offer a lot more in terms of performance.  Same as
>>>>R=3 did when we got to 12-14 plies...  _then_ it might make sense to up R
>>>>once again.
>>>
>>>I do not know.
>>>I did not investigated different R's but I suspect that constant R may be a bad
>>>idea and R should be function of the position.
>>>
>>>I do not see a reason to use R=4 in the future and not to use it today at the
>>>same conditions.
>>>
>>>Uri
>>
>>
>>I adjust R between 2 and 3 already.
>>
>>The reason to use R=4 in the future is easy:  Which would you rather do to
>>reject a move at the current ply...  (a) a search to depth D, or (b) a search
>>to depth D-3, or (c) a search to depth D-4?  That is what the R value is all
>>about.  And it makes a significant difference at deeper depths.
>
>Everything that can be used in the future can be used also today.
>
>If you talk about deep depth you can also today use a rule to search to depth
>D-4 and not D-3 if D is big enough.
>
>I see no reason to wait to the future.
>
>Uri


Two reasons...

1.  R=4 doesn't make a huge difference because the current hardware is not
fast enough to drive the search deep enough to make it matter.

2.  R=4 will produce tactical oversights at today's depths, while R=3 produces
fewer of these.

I personally think that as depth goes up, so can R, with relative safety.  This
based on 8 years of testing this in Crafty...



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