Author: Vincent Diepeveen
Date: 14:16:00 09/10/02
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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. >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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