Author: David Rasmussen
Date: 10:09:24 01/11/02
Go up one level in this thread
On January 11, 2002 at 11:44:39, David Rasmussen wrote:
>[D]2Q2n2/2R4p/1p1qpp1k/8/3P3P/3B2P1/5PK1/r7 w - - 0 1
>
>In the above position, my search tree explodes because of extensions. It takes >
>3 minutes and 42 million nodes to finish an 8 ply search. How does your program
>do?
>
>Any good ideas on how to limit extensions in such a position.
>
>P.S. Solving the position is no problem. It is a simple mate in 5 plies, and is
>found very early on at depth 1 or 2 or so. Still, there must be something
>unsound about my extensions, or at least room for improvement, when this
>position makes the tree explode.
>
>/David
The same thing happens with WAC 161:
[D]3r3k/3r1P1p/pp1Nn3/2pp4/7Q/6R1/Pq4PP/5RK1 w - - 0 1
time nodes depth score pv
00:00:00.17 33kn 05/16/16 ---------------------------------------------------
00:00:00.19 36kn 06/12/12 +MAT7 1. Qxd8+ Rxd8 2. f8=Q+ Rxf8
3. Rxf8+ Nxf8 4. Nf7#
00:00:00.56 122kn 06/17/17 ---------------------------------------------------
00:00:00.59 132kn 07/13/13 +MAT7 1. Qxd8+ Rxd8 2. f8=Q+ Rxf8
3. Rxf8+ Nxf8 4. Nf7#
00:00:07.75 1887kn 07/46/46 ---------------------------------------------------
00:00:07.80 1906kn 08/14/14 +MAT7 1. Qxd8+ Rxd8 2. f8=Q+ Rxf8
3. Rxf8+ Nxf8 4. Nf7#
00:03:25.14 51Mn 08/54/54 ---------------------------------------------------
00:03:25.19 51Mn 09/15/15 +MAT7 1. Qxd8+ Rxd8 2. f8=Q+ Rxf8
3. Rxf8+ Nxf8 4. Nf7#
00:47:45.77 736Mn 09/62/62 2/52 1. Ne8
This is while searching. The search is not finished. Hence the last line showing
only the move being searched right now. The numbers in the "depth" row (x/y/z)
are nominal search depth, max depth at which q-search begins (this can be higher
due to extensions), and max depth at which q-search ends. From the numbers
above, you can see that for ply 8 and for ply 9 up until now, we extend in the
longest line to 54 and 62 plies respectively! That is too much. My extensions
right now are:
Check extension: 1 ply
Pawn push extension to rank 7 (2): 0.75 ply
Recapture extension: 0.75 ply
One Reply extension: 0.75 ply
The sum of extensions at a ply are limited to at most one ply. Although one
reply extension is added _after_ this limiting, as one_reply wouldn't make any
difference at all. I mean, it is only applied in check positions where there is
only one move, and in those positions I already add the check extension. So 1 +
0.75 = 1.75, and limiting this to 1 ply would yield 1 ply. How do you guys
tackle this?
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