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Subject: Re: Null move reductions

Author: Don Dailey

Date: 12:46:09 10/05/98

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On October 05, 1998 at 14:39:57, Will Singleton wrote:

>On October 05, 1998 at 09:37:31, Robert Hyatt wrote:
>>does it quite easily..  if we are doing a 6 ply search, at ply=3 we find a
>>way to rip a piece so that the score is +3.00, at ply=4 we try null-move
>>and subtract an extra two plies from the search depth, which takes us right
>>to the q-search, where the opponent recaptures the piece, so that the null-
>>move search fails high.  I don't look at checks in the q-search, which means
>>my q-search won't see the mate on g7, so we stop the search at ply=3 thinking
>>that BxN is ok, when our opponent will *really* not play pxB, but will,
>>instead, play Qg7#.
>>Next move you see this, but it could be too late...
>Since you don't look at checks in the qsearch, do you have problems with
>positions such as wac002?  Or perhaps that's handled in a different way.

Hi Will,

I think this is a matter of compromise.  Bob's method emphasizes speed.
There is no question that if you do not do checks in quies you will
lose a ply here and there in certain tactics.  But this must be balanced
with what you gain.  Once you have committed to NOT doing checks in
quies, you can seek many other kinds of speedups.  I don't know if Bob is
making the right compromises or not, but the point is that all of this
is trading "this and that" for the "other thing."   If he were forced
to look at checks in quies, then he would probably be delayed in using
his SEE evaluator and also miss out on those speedups.  In a program
like Bob's I would guess this would be a reaonsably big slowdown, and
therefore he may choose to give up the checks to gain the greater
search depth in general.  Of course we will want to hear from Bob on
this but the main point I stress is that computer chess programming
is full of making these kind of compromise decisions.

- Don

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