Author: Johan de Koning
Date: 19:52:02 03/25/04
Go up one level in this thread
On March 25, 2004 at 16:40:26, Robert Hyatt wrote:
>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.
Fair enough, but null moving doesn't fit in your vocabulary.
One solution is to define null moves as part of the reference tree
(a search that utilizes 4. at most).
Another way is to allow searches under 3. After all, null move is an
estimate *and* it is used to disqualify members of M. That's sounds
like pruning! :-) And after hiding the null searches in an (expensive)
black box there is no difference at all.
... Johan
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