Author: blass uri
Date: 16:35:26 10/02/98
Go up one level in this thread
On October 02, 1998 at 18:39:04, Robert Hyatt wrote: >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... my point is that I do not understand why crafty without tablebases does the move Rxb2 at depth 12 If it can see the position of KPP against K then the evaluation without tablebases should prevent it to play it and if it cannot see the position of KPP against K then tablebases cannot help. Uri
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