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Subject: Re: morphy's 17.QxB sac

Author: Dieter Buerssner

Date: 09:32:58 07/13/00

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On July 12, 2000 at 20:30:42, Dann Corbit wrote:

>This position can be used to determine if a computer uses NULL move pruning or
>not.  I am fairly sure that is what is going on here.

To me, this is not to be a null move problem. I tried this with Yace default
settings. On my AMD K6-2 300 with 30 MB hash, it needed 350 s.
Mogens showed a log with about 100 sec. He shows almost exactly 3 times
the Nodes/s, that I get, and has about double hash - so this is consistent.
Then I tried a Crafty like null move algorithm, with higher reduction at
high depth: 240 sec. Then I tried even more aggressive null move with a
depth reduction of 4 at all depths: 180 sec. Then I tried no null move at
all - after 15 minutes without solution I lost patience. With null move,
Yace always found the solution at ply 12, regardless of the aggressifity
of the null move algorithm.

Also, I suspect that this position may not be too objective, when comparing
different chess programs. At the ply before Yace finds the solution, the
moves Qxa6 and Qxf3 are not far apart. Doubling positional scores halfed
the solution time in one test I have done. I guess that tweaking some eval
parameters should give the solution even faster. Of course, the 14 s reported
for Fritz are impressive ...
Which search depth was this for Fritz?

Regards,
Dieter



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