Author: Steve Coladonato
Date: 05:56:13 01/20/00
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On January 19, 2000 at 13:29:23, José de Jesús García Ruvalcaba wrote: >On January 19, 2000 at 09:48:11, Steve Coladonato wrote: > >><snip> >> >>>>Dave, >>>> >>>>Thanks. From this and also what Michel posted, I gather that a TB is some kind >>>>of ordered list based on some criteria that, once a root position is reached, is >>>>searched repeatedly for the next move. And it's structure is not like that of a >>>>tree. >>>> >>>>Steve >>> >>>The tablebase is a giagntic, collision-free hash table. You have a hash >>>function that takes a board position (where all the pieces are, whose move it >>>is, is castling legal, et cetera) and tells you the spot in the hash table that >>>contains the data you need for that position (who is to win, and in how many >>>moves.) >>> >>>It is possible to have an ordered list, and use binary search to find >>>information on the position you are interested in, but hashing is faster for >>>looking up stuff, because no searching is involved. You can find more >>>information on "hashing" in books that deal with computer algorithms. It is a >>>general technique that is often used when data retrieval must be fast, and >>>certain other constraints are met. >>> >>>Dave >> >>Dave, >> >>OK. Now, if the information for the position also contains the best move, > > It does not. Tablebases only store scores, not moves. > >>the >>program would make that move and then do a hash lookup on the position arising >>from the opponent's move. > > Not quite. After receiving the opponent's move, it does a one ply search and >chooses the move which leads to a higher score (I am assuming we are on a root >tablebase position). > >>The assumption is that once a TB position has been >>reached, all possible subsequent positions are in the TB. >> > > Most programs assume this, and thus have problems when there are some >tablebases missing. > >>Am I any closer? >> >>Steve Jose, Thanks. But I am curious as to why the best move isn't also stored. It seems a waste to have the program do a one ply search to determine the best/next move. Steve
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