Author: Robert Hyatt
Date: 15:39:04 10/02/98
Go up one level in this thread
On October 02, 1998 at 15:06:17, blass uri wrote: > >On October 02, 1998 at 13:12:02, Robert Hyatt wrote: > > >>>I understand that tablebases provide -MatNN,+MAtNN and draw scores >>>but I do not understand how can you go to positions that you use tablebases >>>at depth 12 from the initial position because tablebases are for KPP against K >>>or KP against KP and not for positions with more pieces. >>>You need to calculate more than 16 plies to go to positions that you can >>>use tablebases if you do not do special extensions in pawn endings. >>> >>>I thought that If you can see by tablebases that the position is -MatNN because >>>it is KPP against K then you can see without tablebases that the position is not >>>-0.xx because the static evaluation function without tablebases is not -0.xx >>> >>>Uri >> >> >>You are misunderstanding how I use them. Imagine a position with KBN vs K. >>You understand that in that position, crafty will play perfectly, and will win >>with the KBN side, correct? >> >>IE in this position: >> >> +---+---+---+---+---+---+---+---+ >> 8 | *K| | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 7 | | | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 6 | | | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 5 | | | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 4 | | | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 3 | | | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 2 | | | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 1 | K | B | N | | | | | | >> +---+---+---+---+---+---+---+---+ >> a b c d e f g h >> >>crafty promptly says Kb2 Mat25... ok so far... >> >>now lets modify the position to this: >> >> >> +---+---+---+---+---+---+---+---+ >> 8 | *K| *R| *Q| | | | | | >> +---+---+---+---+---+---+---+---+ >> 7 | | | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 6 | | | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 5 | | | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 4 | | | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 3 | | R | | | | | B | | >> +---+---+---+---+---+---+---+---+ >> 2 | | | | | | | | | >> +---+---+---+---+---+---+---+---+ >> 1 | K | B | N | | | | | | >> +---+---+---+---+---+---+---+---+ >> a b c d e f g h >> >> >>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". Or in some variations it sees one black and one >>white pawn being traded, and that also leads to mate in N. > >The difference is that in your example you have a line of 8 plies leading to the >position that you use tablebases and >you have not a line of 12 plies from the position before Rxb2 that can lead to >KPP against K or KP against KP > >because the white king must do at least 9 moves to eat the black pawns >Kxb2,Kc2,Kd3,Ke4,Ke5,Kf6,Kg7,Kxh7,Kxg6 > >Uri I'm not sure what your point is, however. I do quite a few search extensions, and the hash table has the effect of letting the search go deeper than normal as well, in simple endings like this. 9 moves is really 16 plies plus q-search, which means a 12 ply search only needs to extend 4 plies to see that... not difficult at all...
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