Computer Chess Club Archives




Subject: Re: addition

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
>>>>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.
>>  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 :-)
>  martin
>>>>say again - why wouldn't i overwrite mainline nodes under these circumstances?
>>>>  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
>>>>>>>>>>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
>>>>>>>>>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!
>>>>>>  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.
>>>>>>>>  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.
>>>>>>>>>>  martin

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