Author: Dieter Buerssner
Date: 08:46:41 04/02/01
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On April 02, 2001 at 04:47:10, Ulrich Tuerke wrote:
>quite impressive performance by Yace again !
Uli, thanks for the nice words.
>It's probably a question of choosing smart search extensions ?
Yes, I think this is correct. Perhaps not smart extensions, but I think I have
extensions that fit this position. I believe the main problem is to find the
refutation for 1. Ba3 Qxa3. Uri has allready sent a line for this. I get:
814247 5.553 4.59 8t 2.Nh5+ gxh5 3.Qg5+ Kh8 4.Qxf6+ Kg8 5.Qf7+ Kh8
6.g3H Nxd4H 7.e7H Qc1+H 8.Kg2H Qc2+H 9.Kh3H
Qf5+H 10.Qxf5H Nxf5H 11.e8=Q+H Kg7H {HT} {421}
Unfortunately, there are many moves from the hash table (all the moves, that
have "H" appended); these are not allways reliable. However, here they look
right. The line starts with 4 checking moves by white in a row. Also, later,
there are 3 checking moves in a row for black. For such situations, I do some
rather aggressive extensions. Of course, you will be well aware of the fact,
that more aggressive extionsions will in general give a bigger search tree, and
so in many positions can hurt.
Another thing might be quiescence search. I think, the moves starting with 10.
Qxf5 are from quiescence search.
Yace does not have the knowledge mentioned by Uri about the knight moves, that
are needed to stop a passed pawn. I have thought of something like this for
endgames, where the opponent has only a knight and pawns. But I found it too
difficult even there, because the knight may gain tempos by checking moves. With
Qs on board, this looks even more difficult.
BTW. Out of curiosity, I made a small experiment with null-moves. Yace uses
something similar to the double null-move, that was mentioned in this forum
quite a few times. I disabled this. The solution time for this position did not
vary significantly. But when I am using more aggressive null-move (R=3 when
still high search depth is required in the tree, R=2 otherwise; by default Yace
uses R=2 allways), the solution Ba3 is found at depth 12 instead of depth 11.
-- Dieter
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