Author: Ricardo Gibert
Date: 12:34:54 08/03/99
Go up one level in this thread
On August 03, 1999 at 14:28:04, Robert Hyatt wrote: >On August 03, 1999 at 10:28:25, Ricardo Gibert wrote: > >>On August 03, 1999 at 09:00:33, Robert Hyatt wrote: >> >>>On August 03, 1999 at 04:45:07, Ricardo Gibert wrote: >>> >>>>On August 03, 1999 at 04:32:27, Bruce Moreland wrote: >>>> >>>>> >>>>>On August 02, 1999 at 22:47:14, Ricardo Gibert wrote: >>>>> >>>>> >>>>>>Your post is a little ambiguous. Are you saying Nalimov EGTB is a shortest mate >>>>>>EGTB for all the 5 man endings? How would the tables be generated? >>>>>> >>>>>>I would be surprised if all the endings covered by the Nalimov EGTB are of the >>>>>>shortest mate variety. I would also be disappointed for the reason indicated. >>>>>>Some endings (other than KQKR which a computer program can win in about 34 >>>>>>moves) would be "impossible" to win using such a TB due to the 50 move rule. >>>>> >>>>>I would be suprised if the Nalimov tables are *not* distance to mate. The only >>>>>publicly available distance to conversion tables that I know of are the Thompson >>>>>tables. >>>> >>>>Shortest mate EGTB also has the defect of possibly concluding that an ending is >>>>drawn due to the 50 move when it is actually winning. By the way, I think this >>>>issue can be cleared up by noting that "distance to mate" is not necessarily the >>>>same as "shortest mate". >>> >>> >>> >>>first, 50 move draw is _not_ included. How could it be? Because you have >>>_no_ idea what position you will enter the database at... >>> >>>and distance to mate _is_ "shortest distance to mate" absolutely... >>> >>Then this means the EGTB will prefer a mate in 51 without pawns moves or >>captures to a mate in 52 with a pawn move or capture before the 50 move rule >>kicks in. It will draw winning positions. Undesirable and unnecessary. >>Fortunately rare. >>> > > >yes... but this is a problem no matter what. Because the tablebase is just >a file that is indexed by piece location, and it provides mated-in-N, draw, or >mate-in-N. It has _no_ idea about prior positions and what might have >transpired before reaching this position. It can't even tell if this position >is a successor of another position in this file, or if it was reached via a >capture with a zero 50-move counter. prior positions are irrelevant. > >deep mates are going to be a problem in 6 piece files, no doubt about it. It >would be interesting to see if there are already violations of this in the 5 >piece files... > > > >>> >>> >>>>> >>>>>And yes, the tables do suffer from the possible problem that you mentioned, >>>>>although this should be extremely rare in practice. >>>>> >>>>>bruce
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