Author: Christophe Theron
Date: 11:49:09 03/30/01
Go up one level in this thread
On March 30, 2001 at 13:03:14, Robert Hyatt wrote:
>On March 30, 2001 at 12:34:37, Christophe Theron wrote:
>
>>On March 30, 2001 at 03:29:51, Tony Werten wrote:
>>
>>>On March 29, 2001 at 22:38:33, Christophe Theron wrote:
>>>
>>>>On March 29, 2001 at 16:01:51, Tony Werten wrote:
>>>>
>>>>>On March 29, 2001 at 15:12:21, Christophe Theron wrote:
>>>>>
>>>>>>On March 29, 2001 at 14:39:34, Tony Werten wrote:
>>>>>>
>>>>>>>On March 29, 2001 at 14:21:16, Christophe Theron wrote:
>>>>>>>
>>>>>>>>On March 29, 2001 at 13:49:06, Tony Werten wrote:
>>>>>>>>
>>>>>>>>>On March 29, 2001 at 13:31:59, Christophe Theron wrote:
>>>>>>>>>
>>>>>>>>>>On March 29, 2001 at 09:14:57, Robert Hyatt wrote:
>>>>>>>>>>
>>>>>>>>>>>On March 29, 2001 at 06:22:13, Jouni Uski wrote:
>>>>>>>>>>>
>>>>>>>>>>>>On March 29, 2001 at 06:17:50, Alexander Kure wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>>On March 29, 2001 at 04:37:19, Tony Werten wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>>>Hi all,
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>until what depth do various programs probe the tablebases ?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>cheers,
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>Tony
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>Hi Tony,
>>>>>>>>>>>>>
>>>>>>>>>>>>>In London 2000, I let Nimzo 8 play with a depth of 6 plies, but later I came to
>>>>>>>>>>>>>the conclusion that 8 plies might be better overall. This is indeed the default
>>>>>>>>>>>>>setting of NimzoX and Varguz playing on ICC.
>>>>>>>>>>>>>
>>>>>>>>>>>>>Greetings
>>>>>>>>>>>>>Alex
>>>>>>>>>>>>
>>>>>>>>>>>>Sorry one stupid question: is this the first or last 6/8 plys?
>>>>>>>>>>>>
>>>>>>>>>>>>Jouni
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>His statement would make no sense if it were the _last_ 6-8 plies. Those
>>>>>>>>>>>are the ones that kill performance if you aren't careful. The first 6-8 plies
>>>>>>>>>>>don't cost a thing.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>But it could also mean it probes TBs in all the plies except the last 6/8.
>>>>>>>>>>
>>>>>>>>>>Meaning that if Nimzo is doing a X plies search, then the program probes the TBs
>>>>>>>>>>in the tree for all nodes that have a distance from the root below or equal to
>>>>>>>>>>X-6 (or X-8).
>>>>>>>>>
>>>>>>>>>Could be but that would mean, with an average depth of 10 to 12, you'd be
>>>>>>>>>probing the first 4 to 6 ply. I mean, it helps but it could help more.
>>>>>>>>>
>>>>>>>>>That is, not counting extensions, but you if you search 10 ply, you don't know (
>>>>>>>>>at ply 8 ) how many plies are still coming.
>>>>>>>>>
>>>>>>>>>cheers,
>>>>>>>>>
>>>>>>>>>Tony
>>>>>>>>
>>>>>>>>
>>>>>>>>But you know how many plies you have done since the root position...
>>>>>>>
>>>>>>>2 possibilities:
>>>>>>>- We are talking about different things
>>>>>>>- I don't get it
>>>>>>>
>>>>>>>Might be both.
>>>>>>>
>>>>>>>Tony
>>>>>>
>>>>>>
>>>>>>You don't know how many extensions you are going to do, so you just ignore
>>>>>>extensions and assume you are going to search full width the same number of
>>>>>>plies as your iteration number.
>>>>>>
>>>>>>So at iteration 10, stop probing TBs after two moves from the root (assuming
>>>>>>like Nimzo that you don't probe in the last 8 plies of search).
>>>>>>
>>>>>>That is why I say "you know how many plies you have done since the root
>>>>>>position...".
>>>>>
>>>>>But then you don't have almost no depths where you probe. (In your example only
>>>>>ply 1 and 2 )
>>>>
>>>>
>>>>
>>>>Yes, but your NPS does not go too low then.
>>>>
>>>>It's a compromise between speed of search and accuracy of the evaluation.
>>>>
>>>>Don't forget that accessing a TB slot can be as expensive as searching 1000
>>>>nodes (depends on your program). And that many TB accesses are just a waste of
>>>>time because they are not going to have any influence on your main line.
>>>>
>>>>I'm not saying that 8 plies like in Nimzo is the right number (actually I'm not
>>>>even sure that Nimzo does it this way).
>>>>
>>>>In Tiger I stop accessing the tablebases a few plies before I reach the horizon.
>>>>If I don't do that the program gets much weaker because of the dramatically
>>>>slower NPS.
>>>
>>>Make your program slower !
>>>
>>>XiniX is a slow searcher and I'm testing on slow hardware so I hardly notice a
>>>slowdown because of probing. ( Might not be the best solution )
>>>
>>>The idea I have for probing a lot is that if a position is worth being searched,
>>>it's probably worth being probed. ( Unless you're very near to the leafs )
>>>
>>>Hmm, search position normal, then store no nodes in hashtable, then when
>>>searched second time: if n.o. nodes>1000 do probe. I'll have a try.
>>>Maybe combined with: first x ply always probe.
>>>
>>>Positions below current position stored in hashtable can help with enhanced
>>>transposition cutoffs as well.
>>>
>>>I'll put it in my totry book.
>>>
>>>Tony
>>
>>
>>If you search 1000 positions per second and your hard disk is fast enough to
>>make 1000 probes per second, don't hesitate, you can probe everywhere in the
>>tree.
>>
>>But if you can make 100000 NPS, then probing always will weaken your program
>>significantly.
>>
>>That's also why you need 2 days to implement TBs in a program, and 2 months to
>>have them working right (improving the strength of your program).
>>
>>
>>
>> Christophe
>
>
>Note that even though you search 1M nodes per second as I do. I _never_ probe
>at that rate. Because if you only probe for captures that take you to 5 or
>fewer pieces, you eliminate most of the nodes quickly and don't probe there.
>The requirement that Move(ply-1)-> capture and TotalPieces(ply)<=5 _really_
>restricts the number of probes, because if you probe there and you don't get
>a hit, you won't probe anywhere _below_ that node in the tree until another
>capture is made...
I'm also using this condition (capture && nbpiece<=5) and I guarantee I get the
hard disk working real hard in endgames positions.
The result on endgame test suites was a real disaster with this condition only.
So I added a condition not to probe when too close (and beyond) from the
horizon.
Then I also added hand crafted endgame knowledge to decide in which cases a
probe is useless.
The result is that Tiger is hardly slower (in NPS) in the endgame, but still
benefits from TBs.
Christophe
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.