Author: Ulrich Tuerke
Date: 04:32:40 06/30/98
Go up one level in this thread
On June 30, 1998 at 06:33:12, Guido Schimmels wrote:
>Does anybody use a refutation table for move ordering ?
>When you already use killer and history heuristic, is a refutation table
>of any further benefit ?
I think that the term "refutation table" has been used in literature in 2 ideas
with slightly different meanings.
1. There are the "butterfly tables" suggested by Hartmann & Kouwenhoven in 1991,
where whenever a cut occurs you store the corresponding move into a table which
is indexed by the preceding move. I have worked with this for several years. It
seems to me that it does result in a modest improvement in move ordering. The
draw-back is that it's a little bit memory intensive ("cache-hostile"). Omitting
these tables on a K6 makes my program at least 10% faster concerning nodes/sec.
I doubt that the benefit thru slightly improved move ordering is worth this slow
down and I'm seriously considering to remove these tables now.
2. There is another (older) refutation heuristics suggested by Akl & Newborn in
1977, where (provided I remember right) the subsidiary variation to each of the
root moves is stored and used. My prejudice is that this became obsolete with
the use of massive transposition tables cause you have these moves in the hash
table anyway.
My conclusion is that these ideas are worth a try in cases where for some reason
only limited hash tables are available, but in general these attempts are
obsolete. But this is only a personal prejudice, didn't really run huge test
cases, only a few positions (for both of the above cases).
Regards, Uli
>Before I waste my time with excessive testing I would like to know
>about your experiences. Thanks !
>
>- Guido -
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