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Subject: Checks in the Qsearch

Author: Scott Gasch

Date: 13:33:10 06/28/02


I've been experimenting with checks in the qsearch.  While implementing this I
ran across a couple of old posts from Bob who said, in essence: If side to move
is in check in the qsearch but has had a chance to stand pat at a previous ply
in the qsearch then the check is not forced and generating all replies to check
is wasted nodes.

I am struggling with this idea.  If you are in check and have no good way out
your opponent will fail high and you will just stand pat where you could at a
previous ply.  I get that.  So is the idea to only generate responses to check
that have a chance at not failing low?  Maybe only capturing responses and
blocking or king flees?  Imagine you are in check and have no capture responses
so you conclude there is no good way out of check -- is it sound to return -MATE
to force your side to stand pat where it could have at a previous ply?  I
suppose the assumption here is that if you are in check and way below alpha
running away or blocking the check is not going to do the trick and you will end
up standing pat at a previous ply anyway.

Another idea that I read from was that generating non-capturing checks in the
qsearch against a side that has had a chance to stand pat already is a waste.  I
really don't understand this idea and disagree with it.  Imagine black has had
an oppertunity to stand pat but instead plays RxN (N appears hung).  Well this
looks really good unless white then generates Qd4+ forking blacks R and K and
winning the R.  If you neglect to generate checks on a side who has already had
the chance to stand pat you let him get away with RxN and like it.  If the only
reason to add checks to the qsearch is to find mates then I agree -- checking
after a side could stand pat is wasted.  But if the goal is to improve tactical
play then I think this idea is not sound.

Scott



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