Author: Christophe Theron
Date: 14:36:45 03/30/01
Go up one level in this thread
On March 30, 2001 at 15:23:38, Robert Hyatt wrote:
>On March 30, 2001 at 14:42:34, Christophe Theron wrote:
>
>>On March 30, 2001 at 13:00:35, Robert Hyatt wrote:
>>
>>>On March 30, 2001 at 12:28:20, Christophe Theron wrote:
>>>
>>>>On March 30, 2001 at 09:30:06, Vincent Diepeveen 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).
>>>>>>
>>>>>>I don't think that probing the TBs in the first 6/8 plies of the search makes
>>>>>>any sense.
>>>>>
>>>>>Do yo mean this in absolute terms or do you mean this in
>>>>>terms of "doing probes last few plies like qsearch is more important
>>>>>as doing probes in the first 8 plies?"
>>>>>
>>>>>In the first case i would disagree. in the second case i would agree.
>>>>
>>>>
>>>>What I wanted to say is that probing the TBs in the first 6/8 plies ONLY does
>>>>not make sense.
>>>>
>>>>I mean that there must be some mechanism to somehow relate the depth of the
>>>>probing to the depth of the search.
>>>>
>>>>If you are going to depth 25 at this time, you certainly don't want to stop
>>>>probing the TBs at depth 8.
>>>>
>>>>However Alex answered something that is still unclear to me which would suggest
>>>>that in the first 8 plies he does some kind of probe, and he does another kind
>>>>of probe in the next plies. But I can be wrong here.
>>>>
>>>>
>>>> Christophe
>>>
>>>
>>>That is what they do. They load the win/lose/draw tables into memory, but
>>>they don't have them _all_ in that format. They probe the normal tables
>>>early in the search where the cost is low. They probe the w/l/d tables
>>>everywhere else as there is no I/O required. This means that for the w/l/d
>>>tables, you only get a bound on the value and you could get into a never-ending
>>>mate in N loop. But by probing the real tables early in the tree, they will get
>>>the right distance-to-mate scores where it really matters...
>>>
>>>This has been discussed before. The only problem I pointed out is that if you
>>>do all the 3-4-5 piece tables as win/lose/draw, you _still_ need over a gigabyte
>>>of memory to hold the result. That is still too big, and now that we are 40
>>>gigabytes into the 6 piece files, forget win/lose/draw for them.
>>
>>
>>
>>OK I see now.
>>
>>Well it's a smart trick and I guess that storing in memory the WDL TBs for 4-men
>>positions only would already be an improvement...
>>
>>However I wonder how many elo points they get with these WDL TBs... It's quite a
>>programming effort to implement them I guess.
>>
>>On the other hand, if you use the memory required to store the WDL TB for other
>>purposes, like extending your hash tables, maybe you get the same kind of ELO
>>increase?
>>
>>So I wonder if it's really worth it.
>>
>>
>>
>> Christophe
>
>
>Actually you get 'em for free. You just write a small driver program that
>will enumerate every possible piece position, do a few legality checks to
>keep things sane, then probe. If you get a value ==0, store a 0, if you get
>a value > 0 store a 1, if you get a value < 0 store a 2, and continue this
>for all positions. If you are sloppy you use 2 bits per position rather than
>8, which is a 1/4 savings. If you are more clever, since you only have 3
>states, you can put 5 positions per byte. If you want to go nuts, you can
>use 3 bits for every 2 positions and save a bit more, but then probing that mess
>becomes somewhat problematic, since the point is to be fast. :)
I understand that you do not need to rebuild the tables and you can copy the
content of existing tablebases.
What I find a little bit complicated is to deal with all kind of symetry and
piece enumeration stuffs. OK, that's not so complicated, but I find the work a
little bit boring. :)
I prefer to work on search or position evaluation...
>I'm just not personally convinced of the usefulness of this since all the 3-4
>and 5 piece files are 7.5 gigs. That turns out to be about 1-2 gigs depending
>on your compression scheme (this actually might be in error as the 7.5 gigs are
>compressed and I have not tried to think about how the 1.5 bit values would
>compress... as well? worse? better? Don't really want to think about it right
>now. :)) I'm not impressed with loading 1+ gigs of stuff into memory. And
>if you have to probe the 1.5 bit tables on disk, I would have to run some
>experiments to see if it actually pays off to have two sets of tables...
But if they just compress the 4-men tables it's not so big.
As far as I know, all 3 and 4 men TBs are only 30Mb big. If you can compress
them by only 50%, then it's only 15Mb to store in RAM.
So maybe it is interesting with 3 and 4 men TBs.
On the other hand, if you have 30Mb available, you can just preload the standard
Nalimov TBs into the disk cache, so I really don't know if WDL TBs really make a
difference.
Christophe
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