Author: blass uri
Date: 12:06:17 10/02/98
Go up one level in this thread
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
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