Author: Ernst A. Heinz
Date: 11:55:39 01/24/00
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Hi Bill, >How are the Nalimov Tablebases different from the Thompson Endgame Databases? Nalimov: distance-to-mate/mated for *all* positions Thompson: distance-to-conversion for *selected* positions In order to clarify the kind of "selected positions" covered by Thompson's endgame databases, I cite from Chapter 5 of my new book "Scalable Search in Computer Chess" which contains more detailed information about the subject: ``Thompson's databases only host positions where the materially weaker and potentially losing side enjoys the right to move. His databases contain exact results for these positions if the weaker side actually loses. Yet draws and possible wins of the weaker side remain unresolved because the databases do not discriminate between them. Consequently, far more than half of the endgame positions that occur during searches and are suitable for database recognition at all do not apply to Thompson's files on average because either the materially stronger side is to move or it does not win. In theory this gets accounted for by 1-ply searches starting at the positions with the wrong side to move.'' Hope this helps, =Ernst= P.S. "Scalable Search in Computer Chess" now at Amazon.de and MKP online. http://www.amazon.de/exec/obidos/ASIN/3528057327/ http://www.mkp.com/books_catalog/3-52805-732-7.asp :-) Please visit http://supertech.lcs.mit.edu/~heinz/node1.html for more information about the book.
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