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Subject: Re: About history pruning...

Author: Tord Romstad

Date: 11:08:35 10/26/05

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On October 26, 2005 at 12:27:13, Gerd Isenberg wrote:

>On October 26, 2005 at 06:58:41, Tord Romstad wrote:
>
>>This condition is the
>>reason for the name "history pruning", which in my opinion is very
>>unfortunate.  History is just one of several conditions which can be
>>used, and we are not talking about pruning, but reductions.  I prefer
>>the term "late move reductions", but it seems I am quite alone.
>
>Yes, i don't like "history pruning" as well.

Cool.  I am not completely alone, then.  :-)

>What about "right wing reductions" ;-)

Perhaps, but it has political connotations which may not be universally
accepted.  :-)

>Do you apply "late move reductions" only at "expected" cut-nodes or on all-nodes
>as well?

I use them absolutely everywhere, except at the root and when the
remaining depth is less than 2 plies.  I use late move reductions even
at PV nodes.  In principle, I want to be more restrictive, but to my
frustration this always makes my program weaker.  :-(

>>I have found the technique to work even better (especially in tactical
>>positions) with the following enhancement:  If, at the node directly
>>following a reduction, the null move fails low, and the moving piece
>>in the move that refuted the null move is the same as the moving piece
>>in the reduced move, immediately cancel the reduced-depth search and
>>re-search the move with full depth.  The point is that in cases like
>>this, the reduced depth move often contain some serious tactical
>>threat, and deserves a deeper search.
>
>As always - thanks for sharing your ideas and improvements.
>Sounds logical - have to think about the control flow of the search.

Another detail is that this enhancement allowed me to do late move
reductions a little bit closer to the leaves.  Previously I couldn't use
them at remaining depth less than 3 plies without introducing too
many tactical mistakes.  It now seems to be safe to reduce the limit
to 2 plies.

>BTW. what about your strange 10% speedup problem you mentioned some time ago in
>WBF?

For the benefit of readers who don't read the Winboard Forum, I'll
recapitulate the story here:

Some time ago, I tried to remove queen mobility evaluation from
my program.  I expected this to make my program a tiny bit faster,
but to my surprise it made it 10% slower (which is a lot for such
a small change).

>Is it still present and did you find an explanation - or was it only a
>temporary chaotical "phantom", which disappeared after some code changes?

I never found an explanation, and it was apparently just a chaotical
fantom which disappeared after changes in parts of the code which
should have been entirely unrelated to this.  Fortunately, it seems that
the slow situation was the exceptional one.  :-)

Tord



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