Author: Gian-Carlo Pascutto
Date: 09:21:34 01/25/01
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On January 25, 2001 at 11:00:46, Robert Hyatt wrote: >Anytime you reduce the depth, I would call that a "negative" extension... My point was that nullmove doesn't really reduce the depth: it does a _different_ (with nullmove included) search with a reduced depth, and decides based on that whether to cut or not. I do not consider the nullmove search to be part of the normal search, it is just a fancy way of establishing a bound and pruning based on what that bound is. Nullmove prunes, it doesn't reduce the depth (of your _real_ search). If you, for example, would reduce the depth of your main search by a ply if your nullmove failed high, I'd consider that to be a negative extension. The main reason why I make this distinction is that any effect by a negative extension should be circumventable by searching deeper. This is not true for nullmove, because it cuts (based on a dynamic criterion which happens to include searching something _else_ with reduced depth). Vincent's double nullmove(*) _could_ be considered a negative extension, because it will pick up zugzwang's eventually if depth is increased. This is not true for normal nullmove. (*) If it works like I remember...I think that you do two consecutive nullmoves and hence end up in the normal search again? -- GCP
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