Author: Robert Hyatt
Date: 13:40:26 03/25/04
Go up one level in this thread
On March 25, 2004 at 01:56:43, Johan de Koning wrote: >On March 24, 2004 at 11:09:41, Robert Hyatt wrote: > >>On March 23, 2004 at 05:05:56, Vasik Rajlich wrote: > >>>Junior, however, appears to come at the problem of selective search via >>>discussions about this in the CCC archives. Amir has claimed that the best way >>>to search selectively is via extensions. To complete the reductions vs >>>extensions thought from above, an extension strategy will have the profile that >>>most moves have the same basic search depth, while certain special moves will >>>have a higher search depth. The profile of a search based on reductions compared >>>to a search based on extensions will be different. >> >>It is easy to prove that last statement wrong. >> >>You write a program that only does search depth reductions. I write a program >>that only does extensions. I can make mine _identical_ to yours. Where you >>reduce, I do nothing. Where you don't reduce, I extend. IE if you don't reduce >>a check, I extend the check. We search _exactly_ the same tree. > >Indeed, assuming fractional plies, it is rather trivial to build >the same tree using either extensions or reductions. > >But it's better to avoid the term "reductions" since it is confusing. >The real issue is extensions versus *pruning*. Let me define _my_ vocabulary to avoid further confusion. 1. Extension. extending the depth of a move based on some property it exhibits, such as being a check or whatever. 2. Reduction. Reducing the depth of a move based on some property it exhibits, such as not being a capture, check, threat, etc. The two terms are inverses. I can extend the set of moves {X} or I can reduce the set of moves {M-X} and get _exactly_ the same result, to the node. Note that M is the set of all moves we will search. 3. Forward-pruning. Taking some set of moves at the current ply and throwing them out with no additional searching of any kind. 4. Backward-pruning. IE alpha/beta pruning that doesn't change the final result at all. > >Assuming Vasik intended "pruning" in that last statement, he is >quite right: different profiles (called search envelopes by Beal). >And *very* different back-up values. > >To add to the confusion an, earlier (snipped) paragraph from Vasik's: >| Of course, in principle there is no difference between >| selective search via pruning and selective search via extensions, the two >| approaches could be equivalent. >IMHO that is the right words but the wrong conclusion. :-) > >... Johan
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