Author: Poschmann
Date: 00:57:59 10/28/01
Go up one level in this thread
On October 28, 2001 at 02:50:56, Poschmann wrote:
>On October 28, 2001 at 02:19:31, Paul Byrne wrote:
>
>>I've been looking at tablebases lately and was wondering if anyone
>>has ever played with this idea (before I spend too much time on it!)
>>
>>Basically, take the normal (Nalimov or whatever) tablebases in their
>>uncompressed form and divide the mate-in-x or loss-in-x values by some
>>number N. So mate-in-1 through N become (+1) mate-in-(N+1) through 2*N
>>become (+2), etc. Then compress the resulting files as usual.
>>
>>The idea being to reduce the number of different values to make the file
>>more compressible.
>>
>>This would, of course, make life a little more difficult for the engine. :)
>>When the position is not yet into a tablebase, there would be little effect --
>>other than any mate/loss scores being a little inaccurate. Once the position
>>on the board is actually a tablebase position, a short search would have to
>>be done to determine the correct move. For example, if the position OTB is
>>scored as (+5), then one would search for the move that forces a (+4) position
>>the quickest.
>>
>>I did a little test to see if the space savings is worthwhile...
>>Using the kbbkn.nbb/nbw tablebases (something with long mates) and the
>>kqnkn.nbb/nbw tablebases (mostly short mates) with various N's -- the
>>numbers are the percentage of the regular _compressed_ tablebases:
>>
>> N=2 N=3 N=4 N=5 N=10 N=100
>>kbbkn.nbb 84.67 75.00 68.26 63.74 52.08 23.11
>>kbbkn.nbw 82.96 73.21 66.98 62.13 47.80 9.10
>>kqnkn.nbb 64.40 48.51 40.58 31.93 19.21 5.86
>>kqnkn.nbw 63.51 46.43 37.20 28.70 6.36 2.57
>>
>>The last 2 columns were just out of curiousity. :)
>>
>>The question is, how large can N be made while still allowing tablebase
>>positions to be played out in a reasonable amount of time? Don't know (yet).
>>
>>None of this would help for generating tablebases, of course. You still need
>>the normal tablebases to generate the reduced ones. And I'd imagine most
>>engine authors would prefer the full tablebases, but for the average
>>player I don't know they'd notice much difference and could save a few GB
>>of disk space... less stuff to distribute or download too.
>>
>>I suppose a lot of folks have enough disk space for 3/4/5 man tables
>>nowadays, but when the 6 man tables become more complete/common, this may
>>help some.
>>
>>-paul
>
>If a program uses tablebaeses it do it in the following way:
>1. Look into the tablebases to find the current position. For example mate in
M moves.
2. Generate all possible moves in this position. Generate this position.
Look in the tablebases, if this position has a distance of M-1 moves to the
end. If this holds true, select the move. If not, try the next one.
-> Therefore you need the true distances to mate in all possible positions.
Ralf Poschmann
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