Author: Tord Romstad
Date: 07:48:52 10/16/03
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On October 16, 2003 at 10:02:58, Uri Blass wrote: >On October 16, 2003 at 09:18:27, Tord Romstad wrote: > >>I would guess that most strong programs finds the right move rather quickly, >>but that CM9K and Ruffian have one of their few blind spots in this particular >>position. > >Your guess is wrong. This is really surprising to me, but OK. >most programs are different than your program and your program has some >advantages relative to the top programs so the top programs cannot see the >following line in a reasonable time: > >1. Nf6+ Kg7 2. Nh5+ Kg6 3. Bc2+ Kxh5 4. d8=Q Nf7+ 5. Ke6 Nxd8+ 6. Kf5 e2 7. >Be4 e1=N 8. Bd5 c2 9. Bc4 c1=N 10. Bb5 Nc6 11. Bxc6 Nc7 12. Ba4 Nc2 13. >Bxc2 Ne2 14. Bd1 c4 15. Bxe2# >* > >They probably assume that black is winning because black has a big material >advantage. > >I guess that your program extend moves that threat mate in 2 like >10.Bb5 when other programs do not do it(even if they extend mate threat they may >not do it in positions when the side to move has only a bishop and pawn because >they were not designed to solve studies and in games it may be better not to >waste time on checking it). I don't extend for mate threats in 2 moves or more, only for threats of mate in 1 (and only in cases when I am lucky enough to detect the mate threat in the null move search, which of course doesn't always happen). However, threats of mate in 2 will sometimes be extended as an effect of the Botvinnik-Markoff extension. As an experiment, i let my program analyse the same position with the BM extension disabled. The result was rather interesting: The move Nf6+ is still found at ply 13, but the program about 10% more nodes to find it! This is very counter-intuitive to me, but I have observed it in other positions as well. Sometimes Gothmog needs fewer nodes to complete a search to a given depth with the BM extension than without. But still, the BM extension doesn't explain why my engine finds Nf6 in a few minutes, as it was only slightly slower without the extension. If it is really true that other programs have problems with this position, I cannot find any explanation why my program is faster. Apart from the Botvinnik-Markoff extension, I don't have any extensions except those which almost everybody uses. Tord
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