Author: Tord Romstad
Date: 15:01:50 01/28/04
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On January 27, 2004 at 15:42:27, Dann Corbit wrote: >On January 27, 2004 at 14:40:37, Tord Romstad wrote: > >>Hi Dann, >> >>Are you sure it is a good idea to re-search if the first IID search >>fails low? I have never tried this myself, but at first sight it >>doesn't look like a good idea to me. When the reduced-depth search >>fails low, it is likely that the full-depth search will also fail low. >>At fail low nodes, move ordering doesn't matter much, because you have >>to search all moves anyway. > >Because it is used for move ordering, and because the depth is 2 plies below the >current search depth, it is a sure win. The cost is 1/400th of a full search, >and the win is a good guess for the pv node. > >At least when I tested it in Beowulf it worked well. But I did not try it both >ways in Olithink. Very interesting. I always assumed that doing another search when the first reduced-depth search fails low was a waste of time, and never even experimented with anything else. It is probably worth a try for me, too (though it wouldn't surprise me if this is one of the many things which are very different in MTD(f) compared to PVS). In a way, one could say that you and I use the opposite extremes of the spectre. I *never* do another search if the first search fails low, while you *always* do another search. It is possible that the optimal approach is somewhere in the middle. If the reduced-depth search fails by only a small amount, do a re-search, otherwise, drop the re-search. There's lots of scope for experimentation. Tord
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