Computer Chess Club Archives




Subject: Re: Couple of chess programming questions

Author: Vincent Diepeveen

Date: 14:45:55 09/10/02

Go up one level in this thread

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.

>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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