Computer Chess Club Archives




Subject: addition

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
>>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?

>>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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