Author: Vincent Diepeveen
Date: 14:49:52 09/10/02
Go up one level in this thread
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? >>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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