Author: Uri Blass
Date: 11:00:31 07/10/02
Go up one level in this thread
On July 10, 2002 at 11:14:54, Robert Hyatt wrote: >On July 10, 2002 at 02:03:01, Christophe Theron wrote: > >>On July 09, 2002 at 12:48:18, Robert Hyatt wrote: >> >>>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... >> >> >> >>(I tried to post this message earlier but went into server errors) >> >> >>Yes, you are right. >> >>It is due to the high number of null move searches failing high (in your test >>run there are 5 null move searches failing high for one failing low). >> >>The searches that fail low are followed by a normal search (going up to the >>normal depth), and that's why in this case the speedup is bounded. Doing a D-4 >>plies search instead of D-3 plies just before a D plies search is a very small >>saving. >> >>On the other hand if you get a fail high you have saved a lot of time by doing a >>D-4 search instead of D-3. That's right. > >Notice that over the two positions I posted, fail highs are way in the >majority... otherwise null-move would be worthless in the first place. >But even when they don't fail low, a R=4 fails low faster than a R=3 search >will, by a factor of 3x roughly. > >Note that I ran a R=4 just for fun and it was 2x faster overall than R=2~3. >That's certainly worth looking into... 2x is almost another ply. The question is how much speed improvment you get from 4 relative to 3. I suspect that most of the improvement is from 3 relative to 2-3. Uri
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