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Subject: Re: what are the most important Six man tablebases?

Author: Dieter Buerssner

Date: 15:50:23 09/06/02

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On September 06, 2002 at 17:17:55, Tony Werten wrote:

>On September 06, 2002 at 16:58:50, Dieter Buerssner wrote:
>No problem. Point is that kppkpp itself will not help you so much. It might say
>you are winning, but chances are very small you'll checkmate with the 2 pawns so
>you need the conversions as well.

I am not sure. I have no experience with 6-men TBs (besides KNNKNN, which is the
smallest download, and which I used for some tests. But this has obviously no
practical relevance). I am well aware of the TB problems with 5-men TBs and
missing conversion cases. In all such 5-men positions I checked, my simple code
did work well, and never spoiled a win into a draw. (Various things, how to
avoid those probs have been repeated in CCC). Perhaps, to stay with this
concrete example of kppkpp, it will be much more difficult. I could imagine (but
I cannot check - who can?) that there may be very difficult to win lines that
transform to kqpkqp. Perhaps here, the methods helpful in 5-men TB positions
will fail. Still, I would think, that in the big majority of cases, the missing
conversion TBs, should not hurt.

>>BTW with these 6 man tables you probably need a 16 bit counter for distance to
>mate, making them twice as big. (You could do with less extra bits but that
>would kill your compression I think)

I don't totally agree, here, but I see your point. I think, using 16 bit
counters will obviously boost the compression ratio - all those leading zero
bitr. If another more compact encoding is used, (say 10 bit is enough) the
comression will be worse. The overall result may still be similar (you save
those 6 bits, but compress worse. Compared to configurations where 8-bit is
enough: 10/8 is not such a big factor ... But, of course, much will also depend
on the compressing scheme, and on the actual distribution of the distances to
mate).

Regards,
Dieter




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