Author: Vincent Diepeveen
Date: 17:50:01 09/10/02
Go up one level in this thread
On September 10, 2002 at 18:23:51, martin fierz wrote: i always overwrite too, but if you can chose from 8 entries that's a major diff with 2. >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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