Author: Kolss
Date: 05:52:09 11/22/05
Go up one level in this thread
On November 22, 2005 at 07:19:24, Bernhard Bauer wrote:
>It takes quite a lot of time for TogaII 1.1 to solve this simple position.
>Why? And what can be done to become faster?
>
>[D]8/7p/8/p4p2/5K2/Bpk3P1/4P2P/8 w
Hi,
That is a good question. Originally, I thought that tablesbases (TB) and / or
bitbases (BB) would help in this position, as some of the critical positions in
the tree are 5-piece endings. However, when I let Ikarus run without TB or BB,
or with TB (5-piece) but no BB, or with TB and BB (only 4-piece), or with TB and
BB (4-piece plus PP-P), I essentially always get virtually the same results. In
particular, the solution (g4!) is always found in ply 11, and the big fail-high
(to > +3) always occurs in ply 12.
Therefore, I guess that it is most likely mainly due to the evaluation of pawn
endgames and the queen endgame in the other critical variation, although the TB
certainly don't hurt much as well.
The main critical line is:
1. g4 fxg4 2. e4 b2 3. Bxb2+ Kxb2 4. e5 a4 5. e6 a3 6. e7 a2 7. e8=Q a1=Q 8.
Qe5+ (or Qh8+) Kb1 {side comment: the rest could be covered by quiescence
search} 9. Qxa1+ Kxa1 10. Kxg4.
[D]8/7p/8/8/6K1/8/7P/k7 b - - 0 10
This is a 4-piece pawn ending. If a program evaluates this highly in favor of
white (because of the distant black king), it will find the solution easily. If
not, it is much more tricky, as the pawn on h7 will only be captured another 6
plies later (10. ... Kb2 11. Kh5 Kc3 12. Kh6 Kd4 13. Kxh7). Now that is 25 (24)
plies down the tree before any program should see a clear advantage for white
(side comment: which however can be dangerous, as black is lacking only one
tempo to achieve the draw).
One of the other important lines is:
1. Kxf5 b2 2. Bxb2+ Kxb2 3. e4 a4 4. e5 a3 5. e6 a2 6. e7 a1=Q 7. e8=Q.
[D]4Q3/7p/8/5K2/8/6P1/1k5P/q7 b - - 0 7
Note that here, black queened first and now can give some annoying checks. If I
let Ikarus run in this position, the score stays stable for quite a while
(several minutes) at around +1.3 to +1.4.
Depending on how the respective programs evaluate the positions in diagrams 1
and 2, it may be easy or very difficult to find the correct move.
Of course, this is not at all an encompassing analysis, but I hope that helps a
bit to understand what might be going on.
Best regards - Munjong.
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