Author: Brian Katz
Date: 02:42:50 04/17/02
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On April 17, 2002 at 01:25:02, Leen Ammeraal wrote: >On April 16, 2002 at 23:15:47, Tom Likens wrote: >b>>situation as a draw (essentially a case of missing the 2-man tablebase le). >> >>>> >>I recently had what I considered an interesting endgame tablebase bug which >>cost my program 1/2 a point on ICS. The problem occurred when a KR vs. KR >>endgame was reached and the opponent captured the program's rook. Instead of >>grabbing the rook with its king it moved the king away and immediately lost the >>game. Looking at the log file revealed that it had been in the endgame >>tablebases for a while. In fact, the way I structure this is that if I'm not >>in swindle mode and the root position is a tablebase draw then it simply prints >>out the PV to the maximum search depth and returns (skipping the search >>entirely). >> >>The problem was that the EGTB probe code did not recognize the K vs. K I have had a similar problem which occurs in the following position if you are using the 4 disc Nalimov set (Endgame Turbo) [D]1r6/6P1/5K2/6R1/8/4k3/8/8 w - - 0 1 Of course the correct move should be to immediately promote the pawn with g8=Q However, you will find if you are using Fritz 6 and before, and quite probably Fritz 7 (I have not tried this with the Fritz 7 engine), that rather than promote the pawn, Rg3 check will be played instead. The reason for this is that the Nalimov set is missing some important tablebase files, such as KRR KR and others. This being the case, the program does NOT then know the KRR KR endgame (and others) perfectly, so it avoids immediately promoting the pawn. There are others that are also missing which also cause this problem. Make sure you have all the KRP vs KR possibilies such as: KRPKR, KRQKR, KRRKR, KRNKR, KRBKR. The remedy for this is to go into Bob Hyatts wonderful site and download the Tablebase files that are missing. It is as simple as that. Make sure that you download both files for each endgame situation you choose to download. Here is an interesting note: The Crafty program is has the intelligence to play the correct move and immediately promote the pawn even with the missing Tablebase files. I am not sure which other programs out there will have problems with the above mentioned program. Another interensting note: If you only used the tablebases that were included on the Fritz6 disc then this endgame will be played properly. Bob Hyatts site also gives an explanation of the missing tablebase problem. I hope this helps some of you. Regards Brian >>So instead of leaving the tablebases it played a losing move that kept it in >>the tablebases, aarrgghh!! Simple to fix, but it begs the larger question of >>what happens in general if a program has access to an N piece tablebase but >>not all the N-1 piece tablebases that the position could become if a piece or >>pieces were traded off. ... > >I cannot remember having had problems with this situation. But >there is a similar case, which was more serious for me: >the program may be dealing with N-piece tablebases in which >one of the N pieces is a pawn, which is about to promote, >while the corresponding N-piece tablebases with that pawn >replaced with a queen is lacking. The effect was that the >pawn refused to promote. For this reason, I now >temporarily switch off tablebase probing when a pawn is >about to promote. >Leen
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