Author: Uri Blass
Date: 13:30:36 03/16/01
Go up one level in this thread
On March 16, 2001 at 16:22:07, John Hatcher wrote: >On March 16, 2001 at 16:09:53, Dann Corbit wrote: > >>On March 16, 2001 at 16:02:20, John Hatcher wrote: >> >>>Here is a position arising from Rueben Fine's "Basic Chess Endings", No. 309b - >>> >>>[D]r7/4P1k1/3K4/8/8/8/8/5R2 w >>> >>>White wins after 1. Ra1. This solution was found instantly (of course) by both >>>Wcrafty-18.6 (using Winboard) and Fritz6, both using the same 5-piece Nalimov >>>tablebases. >>> >>>But now it gets strange. What if White temporizes first with 1. Rg1+ Kf7, >>>arising at this position: >>> >>>[D]r7/4Pk2/3K4/8/8/8/8/6R1 w >>> >>>Wcrafty-18.6 instantly finds the win after 2. Rf1+ Kg7 (not 2. ...Ke8? 3. Rf8#) >>>3. Ra1, transposing into the first position. However, Fritz6 doesn't see the >>>win!? It's engine output reads: >>> >>>Analysis by Fritz 6: >>> >>>1. = (0.03): 10.e8R Rxe8 11.Rf1+ Kg6 12.Kd5 Kg5 13.Rf7 Rd8+ 14.Ke5 Re8+ >>>2. = (0.00): 10.Re1 >>>3. = (0.00): 10.Rh1 >>>4. = (0.00): 10.Rd1 >>>5. = (0.00): 10.Ke5 >>>6. = (0.00): 10.Kd5 >>> >>>How can Fritz6 see the win in the first position and not see it in the second? >>>The most obvious move, 2. Rf1+, isn't even listed in the engine output!? >>> >>>What's going on here? Can anyone duplicate this strange output? >> >>That is very odd. Every engine I tested (which knows about tablebase files) >>found it immediately. >> >>I have the 5 men files. Maybe Fritz has only the 4 men files available? > >No, Fritz6 and Wcrafty-18.6 are accessing the same 5-piece tablebase files. > >Just to be certain, I run the native Chessbase version of Crafty-18.03 under >Fritz6 and it instantly found the win in the second position after 2. Rf1+. > >Fritz6 accesses and uses the 5-piece tablebases just fine, as evidenced by the >fact that it instantly found the win (1. Ra1) in the first position. I've been >using the 5-piece tablebases under Fritz for a while, and they've always worked >just fine. > >Even stranger, in the first position, Fritz announces mate in 'x' moves if White >plays 1. Rg1+ instead of 1. Ra1, but then "loses" the mate when it reaches the >second position. I'm stumped. > >JOHN The reason is clear. Fritz calls the tablebases everywhere except cases when the remaining depth is small. I guess that after 1.Rg1+ it can see the mate because it never reaches the position after Kf7 Rf1+ Kg7(it probably looks at the tablebases when the remaining depth is 3 so it does not have to search to depth 3) After 1.Rg1+ Kf7 it cannot see the mate because remaining depth of 2 plies is too small for it to look at the tablebases so it can see repetition and evaluates the position as a draw. Uri
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