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Subject: Re: Extend or not extend in a nullmove tree

Author: Robert Hyatt

Date: 08:26:52 06/08/98

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On June 08, 1998 at 03:03:37, Roland Pfister wrote:

>Last week we discussed what to do and not do in a nullmove subtree.
>My program Patzer used to not extend in such a branch. Bob argued
>against it and it sounded ok to me.
>
>At the weekend I tried both versions and the result is that if Patzer
>doesn't extend it is a little bit faster, but not much. But in some
>positions it sees the solution one iteration later!
>
>So I changed my program to extend even in nullmove branches.
>Thanks Bob.
>
>Roland

Here's another "crazy one" to try.  In Cray Blitz, I very carefully
chose
where to try a null move (non-recursive, only allowing *one* in any one
path).  I never tried it on a "PV" node for example, since such a node
can
not really have a null move played.  And to do so would mean that the
null
move search might fail high (as we hope) or it might return a score
between
alpha and beta, but we couldn't keep it.  So I simply disallowed it.

I started off doing this in Crafty, but by accident, disabled the test,
and
the search ran faster overall.  That is I *always* try a null-move
search,
except for when the "null-move transposition table trick" says to not
try
one.  And surprisingly, it was/is faster.  If you aren't doing this, you
should try it...  and let me know if it is faster or slower.  I was
surprised,
and it simplified the code a bit as well since I no longer have to worry
about
whether a node is "ALL", "CUT" or "PV" now... and that code is now
gone...



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