Author: Dan Homan
Date: 12:16:59 08/19/98
Yesterday I asked a question on ICC about extending simply
for being in the principle variation, the idea being to detect threats a
little earlier at the expense of possibly missing a good tactical shot.
Bruce Moreland suggested that I test this with a tactical test
suite to get an idea for how much tactical zip I lose by doing this, and
to bin the results with respect to solution time to give additional
information. Below are the results of the test I ran.
My implementation of the extension is to simply add some
fractional ply extension if we are in a pv node at depth = 1 or
depth = 0. I determine if this a node is a pv node by simply
comparing alpha and beta to the root values of alpha and
beta.
For my program it turns out that if I use 3/4 ply fractional extension,
this adds 4 ply to a full pv line, and if I use a 2/3 ply extension, this
adds 2 ply to a full pv line.
To test this idea, I used the subset of the ECM suite posted by
Jouni Uski a couple of days ago. The total problem set is 231
rather challenging problems. I ran each problem for 60 seconds
on my Compaq Presario at home (it has a strange processor, but
as a practical matter is about 15% slower than a P133).
Solutions were only counted as correct if they were held until the
end of the 60 seconds search period.
Here is a table of the problem solution times for a 4 ply effective
extension in the pv, a 2 ply effective extension, and no extension.
# of problems solved
time bin No pv 2 ply pv 4 ply pv
(seconds) extension extension extension
0 - 15 30 30 25
16-30 17 13 20
31-45 13 13 12
46-60 5 8 4
---------------------------------------------------------------------------------------
totals 65 64 61
So, as a general rule, the extension slows down the solution
times. In order to gauge this properly I would also need a good
"avoid move" testsuite to see if the pv extension would
substantially decrease the amount of time to see that a tempting
move is really bad.
- Dan
P.S. My game results on ICC seem no worse with the extension than
without it, but I am not sure that it is better.
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