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Subject: Re: addition

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
>>>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 :-)


>>>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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