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Subject: Re: Bitbases- What are they? Tablebases?

Author: Vincent Lejeune

Date: 01:52:12 12/07/05

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On December 06, 2005 at 15:06:52, Dagh Nielsen wrote:

>On December 06, 2005 at 05:42:11, Vincent Lejeune wrote:
>
>>On December 06, 2005 at 05:24:26, Steve Lim wrote:
>>
>>>On December 06, 2005 at 05:21:34, Daniel Shawul wrote:
>>>
>>>>On December 06, 2005 at 05:15:54, Steve Lim wrote:
>>>>
>>>>>Title says it all. Am just wondering how they differ from Eugene's EGTBs?
>>>> They store only Win Draw Loss information, hence they are smaller and some
>>>>of them can be loaded in to RAM, which makes them faster.
>>>>
>>>>>
>>>>>Thanks.
>>>
>>>
>>>Ahhh.. similar to the old Distance to Conversion vs Distance to Mate.
>>>
>>>This is DTC I guess.
>>
>>I'm trying to be more clear ...
>>
>>In the Bitbase endgame file only results is store, so there's only 3 values
>>possible for each position 1) win 2) lost 3) draw
>>In comparison, in the 5 pieces Nalimov files there's 256 (255?) possible value
>>from -127 to +127 (-127 = mated in 127 moves ; 0 = draw ; +127 = mate in 127
>>moves, not very sure about this values, but it's the logic)
>>
>>In bitbase one can store 4 positions per bytes but one don't know the best move.
>>In Nalimov (5 pieces) one can store 1 positions per byte but one knows the best
>>move(s).
>>
>>remark :
>> I pointed Nalimov "5 pieces" because some 6 pieces endgame require more than 1
>>bytes (mate > 127 moves). On one side that means that more pieces on the board
>>give bigger size difference between Nalimov and bitbase but the drawback will be
>>that with the bitbase, computer will not be able to find the mate because it's
>>so long that the file with draw/win/lose will not be enough to find the path to
>>the mate in 1.
>
>
>Hi, I'm not sure I understand all the advantages of bitbases in full, but I'm
>just wondering if one could not use an approach like this:
>
>(1) Use bitbases during search
>(2) Once won/lost position is reached, switch to Nalimov table bases.
>
>The point would be to speed up things,

The very main advantage is space required, when you need 400 GB of Nalimov data
to know the right issue of an endgame, only 100 GB (or may be less) of bitbase
is required.

> but I don't know if I got something
>wrong.
>
>Regards, Dagh Nielsen



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