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Subject: Re: New(?) search idea.

Author: Bruce Moreland

Date: 23:30:48 01/21/98

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To clarify, all of this is about what happens at the root.  It has
nothing to do with what happens inside the tree.  To do this inside the
tree would be wrong.

I think it's probably wrong at the root, too, but that's my problem -- I
don't want to take the time to do the experiment, most of the time I
have a backlog of my own ideas to try, and I don't have time to track
down everything like this.  If someone else wants to do the experiment,
that would be great, and would be useful to the rest of us regardless of
how it turned out.

This idea might be related to some other techniques, by the way, there
are algorithms that do zero-width searches on every move at the root,
and try to close in on the true value.

I don't know exactly why the PV (first) move takes so long to resolve,
but I can guess.  I think that it takes a while to resolve because the
window is wide, and the value will probably be within the window.

From experience it seems like you get a faster result if you have a
narrow window and the move fails low.  If someone wants to prove this,
cool, there is probably an easy proof for the mathematically inclined.

This is what will happen to the root successor moves if the poster does
his backwards search, I think.  I think he'll end up showing that the
root successor moves are bad before he gets around to understanding the
first root move, and assuming that he does the exact same searches as
he'd otherwise do (he won't, but I don't think this will matter much),
he'll probably take about the same time in total to do all this.

This could be a win if one of the alternates is great, and you have
enough time to get to it, but not if you search the PV first.

But there are problems, too.  It's complicated and you might end up
having to search some successors more than once.  The time spent doing
extra work in the general cases could outweigh the cases where you find
a shot right before time expires.

Something this might sacrifice is something that Bob pointed out in a
paper years ago -- that if the PV move is going to fail low, it's going
to do it pretty quickly.  So if you try to find the shots faster, you
might miss the fail lows more often then you should, and end up failing
to extend time in crucial cases.

I don't know how this would all weigh out.  This needs to be shown
experimentally, I think.

bruce



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