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Subject: extensions + reductions + pruning = confusion

Author: Johan de Koning

Date: 22:56:43 03/24/04

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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*.

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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