Author: Robert Hyatt
Date: 17:43:41 10/02/98
Go up one level in this thread
On October 02, 1998 at 20:26:08, blass uri wrote: > >On October 02, 1998 at 18:36:45, Robert Hyatt wrote: > >>On October 02, 1998 at 15:23:11, blass uri wrote: >> >>> >>>On October 02, 1998 at 13:12:02, Robert Hyatt wrote: >>> >>>> >>>>In this position. crafty says Be4+ Mat34, with a 2 second search. How did >>>>it do that? like this: >>>> >>>> 8 2.03 Mat34 1. Be4+ Ka7 2. Bxb8+ Ka6 3. Bb7+ Qxb7 >>>> 4. Rxb7 Kxb7 >>>> 8-> 3.27 Mat34 1. Be4+ Ka7 2. Bxb8+ Ka6 3. Bb7+ Qxb7 >>>> 4. Rxb7 Kxb7 >>>> >>>>What it did was to search deeply enough to see that it could trade bishop >>>>and rook for the opponent's rook and queen, leaving it in a KBN vs K position. >>>>And after searching the 8 plies into the future (as it did above) it then found >>>>the endgame database position and said "aha, Mate in N from this point." >>> >>> >>>> >>>>This is why my current version (15.21) won't play Rxb2, because it can see >>>>deeply enough into the future to see the white king eating the black pawns >>>>and that gives "mate in N". >>> >>>If it could see this then without tablebases the evaluation was instead of -0.xx >>>big advantage for white because it could not see the mate but could see the >>>position of KPP against K >>> >>> Or in some variations it sees one black and one >>>>white pawn being traded, and that also leads to mate in N. >>> >>>I do not think that there are logical lines to go to KP against KP in the >>>example that I gave >>> >>> >>> >>>Uri >> >> >>Look at the final position in the short variation you gave. White's king >>is 3 files closer to the pawns than the black king is, and black gets to >>watch while the white king penetrates the black kingside and shreds it... >> >>So I'm not sure what you aren't "seeing" there... > >In the final position it is easy to see that white is winning the problem is in >the position before trading rooks. > >I checked the position with crafty after Rxb2 Kxb2 without tablebases >and it needs to go 18 plies deep to see that the position is worse than -2.xx > >It is easy to compute many plies deep in a pawn ending but the real problem is >before the pawn ending and I do not understand how hash tables can help and how >can you compute 15 plies deep in rook ending when my pentium200MMX cannot finish >12 plies in 20 minutes. > >Uri first my machine is at least 6x faster... this being a 4 cpu pentium pro machine, where a Pentium 233/mmx is about .7 times as fast as a single pentium pro... second, you asked a specific question, and I tried to answer it. In that position, my version (15.21 with some new extension things being tested) will *not* play rxb2. In order to answer that question, I had my version search *only* Rxb2, and not all legal moves, which makes it much easier to get to 15 plies. And by the time it got to 15, it still was not liking the move, as I said... I may not have been clear in explaining what I had done, but I simply told it to only consider rxb2 to see if the score would jump at 12 or 13 as you suggested. I can only speak for this version, which may or may not have bugs, but this version says rxb2 loses, at any depth I tried it on. That's all I can say... this version will *not* play that move at present...
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