Author: Robert Hyatt
Date: 08:33:12 02/14/03
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On February 14, 2003 at 00:51:54, Antonio Dieguez wrote: > >>All that is critical is that you store the same depth you probe with. If you >>do some extensions before storing, you had better do those same extensions >>before probing. IE if you don't, you are going to introduce some huge artifacts >>that will break things. > >It seems that is not all what is critical because precisely you may don't know >if the same extensions will happen in both ocassions. That is dangerous. The hash table stores a "position" and a "value". If the "position" is different, then the value is useless. If you apply different extensions in the _same_ position, then how can you possibly use a hash table hit, since you won't know which "case" it should really be matching. The usual (and correct) way of hashing is to probe in the search, _before_ you do any extensions or anything at this specific ply. And when you store, you store the _same_ depth you had when you entered search and did the probe that failed, so that the next time you probe, and get a match, it makes sense to use it. Any other approach is going to produce instabilities. > Probing and storing with >the _new_ depth remaining solves that at once, but some others have said is a >little bit slower for them because they want to probe the hashtable first to >hopefully avoid the looking-for-extensions fase. Anyway many things have their >good and bad sides. The only requirement is that for a position P, with draft D (plies remaining before you drop into q-search), that D _must_ be the same when you store, as it will be when you probe for a match for P later. Any other approach is going to produce wrong results. > >>Either you will be cutting off when you should not, or not cutting off when >>you should. The former will cause the search to become very unstable. The >>latter will make it slow. >
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