Computer Chess Club Archives




Subject: Re: addition

Author: martin fierz

Date: 20:05:56 09/10/02

Go up one level in this thread

On September 10, 2002 at 20:50:01, Vincent Diepeveen wrote:

>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.

i just checked my code and noticed i had actually turned off that it always
replaced. hmm. i ran some tests, with N=2 or N=8 probes, and the always replace
scheme was better than the don't replace scheme, by about 9% (N=2) and 12%
(N=8). i wonder why i turned it off :-(


>>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

This page took 0.01 seconds to execute

Last modified: Thu, 07 Jul 11 08:48:38 -0700

Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.