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Subject: Re: Checks in the Qsearch

Author: Uri Blass

Date: 22:56:15 07/08/02

Go up one level in this thread


On July 08, 2002 at 23:34:52, Robert Hyatt wrote:

>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...

I see no reason to wait for the future.
If R=4 is good only for depth>15 then people can use it also today only when the
remaining depth is bigger than 15.

Uri



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