Author: Robert Hyatt
Date: 09:48:18 07/09/02
Go up one level in this thread
On July 09, 2002 at 03:40:31, Christophe Theron wrote: >On July 08, 2002 at 23:32:09, Robert Hyatt wrote: > >>On July 08, 2002 at 13:58:51, Christophe Theron 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. >>> >>> >>> >>>It doesn't matter to what depth you are searching. >>> >>>Increasing R can in the best case only give a minor speedup. >>> >>>The speedup you can get by increasing R is bounded to a few percent. >> >> >>No it isn't... This is _still_ an exponential problem. The problem at >>present, with R=4, as that there are not many nodes where that is better >>than R=3 since either one takes depth to zero. When you start averaging >>18 plies, then R=4 has 14 plies to influence the search, not just 8 as it >>does with 12 ply searches... >> >>Just try R=1, then R=2, then R=3 for shallow and then deep and then deeper >>searches. R=3 doesn't do much for blitz at all. For longer games, it begins >>to make a difference. I suspect R=4 will do the same thing. Again, it is >>not just a "few percent" when you refute a move with a depth D search vs a >>depth D-3 search vs a depth d-4 search. The D-4 search will take 1/3 the >>time of the D-3 search. That is pretty significant. > > > >You are right in the case where the search following the null move fails high. > >The speedup is limited to a small percentage in the case where the null move >search does not fail high. > >So it all depends on the percentage of fail high and fail low after a null move. > > > > Christophe > No. Why should it? If you do a null-move search, does it _matter_ whether it fails high or fails low? You _still_ had to do it. So the issue is "how big is the tree?" Here is some sample data from crafty: nodes searched: 9.25M nodes searched below a NULL move: 7.75M null_move searches failing high: 1.02M null_move searches failing low: .235M Another position: nodes searched: 15M nodes searched below a NULL move: 5.5M null_move searches failing high: 2.0M null_move searches failing low: .5M That is why I said "this is not about a few percentage points." First position researched with R=4, just for fun: Nodes: 4.7M below NULL: 3.3M fail high: .624M fail low: .138M Going from R=2~3 to R=4 reduced the search time by 50%. _very_ non-trivial... > > > >>>Just evaluate the time you are spending in null move searches currently. The >>>best you can do by increasing R dramatically is to reduce this time to a value >>>close to 0. That means a potential speedup of a few percent at best. >> >>It is non-trivial. And going 4-6 plies deeper will make it more non-trivial. >> >> >>> >>>On the other hand you are opening the door to huge tactical oversights. >> >>That is what everyone said on the R=2 issue earlier. And then R=3, although >>some use it exclusively now. R=4 is just another "step"... >> >>> >>>It might be possible to crank up R to a value of 5 without doing major mistakes >>>too often, but as it will give an insignificant speedup not even able to >>>translate to 2 elo points, I do not see why anybody would want to take the risk. >> >> >>As I said, when the typical depth is 18, it won't be a couple of percent >>in general... >> >>I don't see anything to suggest a "diminishing return" here for larger R >>values... >> >>The risk is another thing however. But again, deeper searches tend to >>mask the risk. At least in my testing... >> >> >> >>> >>> >>> >>> Christophe
This page took 0.01 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.