Author: Robert Hyatt
Date: 19:10:29 10/02/98
Go up one level in this thread
On October 02, 1998 at 21:22:34, John Coffey wrote: >On October 02, 1998 at 20:47:47, Robert Hyatt wrote: > >>On October 02, 1998 at 19:35:26, blass uri wrote: >> >>> >>>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 >> >> >>because crafty doesn't evaluate KPP vs K or KP vs KP as won, in that >>position. Which is the point here. If the black king couldn't get >>into the square of the white pawn, it would say this is lost instantly, >>or if it could get to KP vs K it can evaluate that perfectly. But not >>KPP vs K or KPP vs KP or whatever... >> >>And tablebases introduce a new bit of data, namely that white is not a >>pawn ahead, but that white is *mating* black. The difference is in the >>value of the evaluation. With the tablebase it is perfect and says mate. >>Without it, it just counts pawns and comes to the wrong position. Without >>tablebases, my current version will play rxb2 at depth=10, because of the >>new extension stuff I am doing. But with tablebases it won't play it ever. > > >That is great. Don't tablebases involve a disk access? If so, how do you >prevent them from slowing down your program? Are you checking the table-bases >at every leaf of the tree? (assuming that it is the right kind of position.) > >Does the time saved not having to search the tree make up for the time it takes >to access the tablebases? > >Thanks in advance, > >John Coffey there is a trick: You only probe *after* making a capture that takes the total pieces to 3 or 4, or else 5 with the specific case of KR*KR left. Doing this is slower than normal searching, but the perfect information it returns does way more than offset the slower speed...
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