Author: martin fierz
Date: 15:23:51 09/10/02
Go up one level in this thread
On September 10, 2002 at 17:49:52, Vincent Diepeveen wrote: >On September 10, 2002 at 17:45:55, Vincent Diepeveen wrote: > >>On September 10, 2002 at 17:36:49, martin fierz wrote: >> >>>On September 10, 2002 at 17:16:00, Vincent Diepeveen wrote: >>> >>>>On September 10, 2002 at 16:06:51, martin fierz wrote: >>>> >>>>I need to refer to extensive proof i wrote down at CCC >>>>which refuted that you overwrite the mainline. >>>> >>>>For a search of 20 ply with a loading factor which is pretty >>>>high, it is still true that with near sureness you have a >>>>19 ply line at least (assuming no extensions otherwise >>>>the line is longer). >>>> >>>>That's true for bounds too of course. >>>> >>>>The chance you overwrite a search depth of 1 ply left >>>>is considerably smaller than you overwrite something of >>>>0 ply left. >>>> >>>>In fact i do 8 probes. >>>> >>>>What loading factor do you talk about here, then fill in the >>>>chances. >>> >>>i'm talking about doing a search of ~10N nodes for a hashtable with N entries. >> >>First of all i don't know the level in checkers, but in international >>checkers it's about 60 moves in 1 hour. Or 90 seconds a move >>initially (of course exchanges are for free). >> >>I don't see how i get a loading factor of 10 there at all, which is >>a *huge* loading factor. With 12 bytes an entry at my dual k7 >>i have about 35 million entries. Well i don't get 350 million nodes >>in a search of 90 seconds at all. >> >>Anyway, to use your doom scenario >> >>But for 8 probes it means you have at 0 ply a chance it isn't overwritten. >>But how many nodes with depthleft of 1 ply do you have? right way less, >>we're not counting qsearch here obviously. >> >>how many nodes with depthleft 2 ply do you have? right even less than >>1 ply. In fact about a bit more than your branching factor less about. >> >>Get the math idea? >>For a full written out chance see my writings elsewhere. > >I hope you realize this is only if you do 1 probe. For 8 probes >there is an additional thing that gets the chance smaller: > >at depthleft==1, > >suppose your hashtable is filled with about 50% searches of 1 ply >left (which would be an insane filled hashtable already). > >What is the chance i overwrite my search result here over another >1 ply left situation? > >Right that's another 1/2 ^ 8. > >So > a) chance that bigger depths get overwritten is real small > b) chance it is still in the hashtable is huge. > >loading factor = 10 is insane high. > >You use very small hashtables always or play at 10 minutes a move? > >If so why? thanks for the explanation. i understand what you mean now. the reason i use smaller hashtables than you think i should is that in checkers you have an 8-piece database, which is 4GB in compressed form. you want to probe that in ram, so you load most of your ram with that database - you just get more out of it than from more hashtable. i only use 2 probes in the HT instead of 8 as you do. i tested this a lot and it gave better results speedwise on normal time controls. for longer time controls it probably would be a good idea to adjust that... my hash replacement scheme seems to be different than yours. when i do an N-fold probe of my table, i ALWAYS overwrite the least important of the N stored values. even if i replace it with a less valuable entry. i tested this and it worked better than not storing if you don't find a less valuable entry. i found that weird, but that was what my test said... obviously, under this scheme i can overwrite pv nodes easily under the high load conditions described. maybe you are right and my hashtable management sucks. maybe my test was broken. let me repeat it...i have a compile switch for these two replacement schemes :-) aloha martin >>>say again - why wouldn't i overwrite mainline nodes under these circumstances? >>> >>>aloha >>> martin >>> >>>>>On September 10, 2002 at 15:41:42, Vincent Diepeveen wrote: >>>>> >>>>>>On September 10, 2002 at 15:19:21, martin fierz wrote: >>>>>> >>>>>>>On September 10, 2002 at 14:45:27, Omid David wrote: >>>>>>> >>>>>>>>On September 10, 2002 at 14:30:56, martin fierz wrote: >>>>>>>> >>>>>>>>>On September 10, 2002 at 09:26:14, Eli Liang wrote: >>>>>>>>> >>>>>>>>>>A couple of chess programming questions: >>>>>>>>>hmm, i only wrote a checkers program, but here's my take: >>>>>>>>> >>>>>>>>>>(1) Are there any uses for ProbCut and/or Multi-ProbCut in chess positions where >>>>>>>>>>the variance of leaf-nodes is low? >>>>>>>>> >>>>>>>>>i've tried multi-probcut and it works well in checkers. i never tuned it as much >>>>>>>>>as my own pruning algorithm, and it doesn't perform quite as well - but it is BY >>>>>>>>>FAR better than no pruning. i'll be trying to tune it in the near future. for >>>>>>>>>games where the eval doesnt swing wildly, MPC is a fantastic algorithm. >>>>>>>>> >>>>>>>>>>(3) Reading Aske Plaat's search & re-search paper, it really seems like mtd(f) >>>>>>>>>>is something of a magic bullet. But I note it seems that more programs don't >>>>>>>>>>use it than do (for example Crafty). What is wrong with mtd(f) which Plaat >>>>>>>>>>doesn't say? >>>>>>>>> >>>>>>>>>i'm using MTD. i tried windowed search, PVS and MTD. in my tests, in long engine >>>>>>>>>matches, MTD performed marginally (no statistical significance...) better than >>>>>>>>>PVS. it typically searched a low 1-digit % less nodes for a given depth than >>>>>>>>>PVS. >>>>>>>>>i don't know how to get a PV out of MTD. in normal searches, a pv node is where >>>>>>>>>the value is > alpha but < beta. in MTD, you never get this condition. >>>>>>>>>retrieving a PV from the hashtable is possible, but in all probability, you will >>>>>>>>>not get the full PV. which is real bad for debugging if you want to know what >>>>>>>>>the program was thinking at the time... i once asked here how to get a pv from >>>>>>>>>MTD but got no answer - and if you can't get the pv, then that is a major >>>>>>>>>drawback. >>>>>>>> >>>>>>>>I haven't tried getting the PV out of MTD(f), but just a thought: why should >>>>>>>>there be any problem in getting the PV out of hash table? Play the first move, >>>>>>>>update the position, get the next best move from hash table, and so on... ?! >>>>>>> >>>>>>>there's no problem with that except that on any reasonably deep search, you will >>>>>>>not have been able to store all pv nodes in the hashtable. so you end up with a >>>>>>>search which says it was 23 ply deep and have e.g. 15 pv moves. if you just want >>>>>>>to display it for the user, that's fine. but if your program plays a bad move, >>>>>> >>>>>>but then your hashtable management sucks ass, sorry to say so. >>>>> >>>>>but you don't use MTD! which means you *know* when you have a pv node, because >>>>>"pvnode <=> alpha<value<beta". and then you can make sure it doesn't get >>>>>overwritten in the hashtable. if you use MTD, you don't have this information - >>>>>all your hashtable entries are either lower or upper bounds... so how do i know >>>>>which ones i have to keep? i'd really glad to learn how to do this :-) >>>>>so if you can tell me how to do it instead of saying i suck (well possible...), >>>>>i'd love to try! >>>>> >>>>>aloha >>>>> martin >>>>> >>>>> >>>>>>I get in Napoleon also only mainlines out of hashtable (with pvs) >>>>>>wasting system time in the search to update all kind of stupid >>>>>>arrays for it is a waste of time, and the next iteration you get >>>>>>true bounds, so you can't get the mainline in arrays anyway (mtd >>>>>>is different here). finding a win in 50 ply is no problem to display... >>>>>> >>>>>> >>>>>> >>>>>>>and you want to know what line it was considering as being best, e.g. because >>>>>>>you want to know if your static eval is bad in the final node of the pv, you >>>>>>>can't do it. IMO debugging your program and finding eval problems like this is >>>>>>>MUCH more important than something like 5% more speed. >>>>>>> >>>>>>>aloha >>>>>>> martin >>>>>>> >>>>>>> >>>>>>>> >>>>>>>>> >>>>>>>>>>(6) Has anyone found any real "practical" benefits to fractional-ply extensions? >>>>>>>>> >>>>>>>>>yes. i tried recapture extensions of different depth, and half a ply gave the >>>>>>>>>best result. don't ask me why, it's just an observation. >>>>>>>>> >>>>>>>>>aloha >>>>>>>>> martin
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