Author: Robert Hyatt
Date: 16:06:58 01/25/01
Go up one level in this thread
On January 25, 2001 at 12:21:34, Gian-Carlo Pascutto wrote: >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 The point of a double-null is that if it is my move, and I pass, the search might actually fail high because not moving wins. If I follow this null move search by one for you, yours will also fail high if it is a true zugzwang position, and if you return beta, my null-move search will fail low and I keep searching normally..
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