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Subject: Re: Singular Extensions, Nullmove deepsearch

Author: Robert Hyatt

Date: 05:11:04 02/16/99

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On February 16, 1999 at 04:45:43, Frank Schneider wrote:

>I experimented a little bit with nullmove deepsearch extensions and with
>singular extensions and now I have some questions:
>
>1. In all my tests the searchtree (#nodes to finish n iterations) increased
>   by a factor of 1.5 to 4. Although testresults were interesting I believe
>   this is too much. What are your experiences?

when I added singular extensions to Cray Blitz, the 'cost' was one ply.
which was about a factor of 5 in speed or nodes.


>
>2. Is it correct to assume that singular extensions work best if there are
>   only few other extension heuristics.


not at all, but you have to be careful as it is possible to over-extend and
drive the tree wild...  Getting out of check is not singular 99% of the time,
so discarding that would cause tactical trouble....  others would probably hurt
also.  IE in CB I didn't take anything out...  but you do avoid the singular
test in some cases (in check with only one legal move is obviously singular,
but I already extend for one-reply so the singular test doesn't happen.)




>
>3. How would you describe the difference between nullmove deepsearch extensions
>  (Donninger) and the nullmove threat detection by Deep Thought?

The ideas are similar, based on the result the null-move search returns.  I
found this not particularly good around version 8-9 in Crafty.  I tried
both singular and null-move threat extensions, and didn't like them back then.
But hardware has come a long way, so that giving up a ply now would not kill my
performance.  Singular extensions (at least a fairly easy to implement version)
is being tested right now by one crafty clone on ICC.



>
>4. Who uses
>   - singular extensions
>   - nullmove deepsearch extensions
>   - nullmove threat detection
>
>5. What is the best (easiest) way to implement singular extensions?
>

if you mean 'real singular extensions' there is only one way to do this,
as explained in the deep thought extension article.   It is non-trivial to
do right, otherwise you have to sort thru a lot of search inconsistencies
causes by a move extending at ply=n, but not at ply=n+1, etc..

I don't know of anyone using real singular extensions other than Deep Blue
and Cray Blitz (this being both PV-singular and FH-singular extensions).




>
>Thanks in advance,
>
>Frank



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