Author: Christophe Theron
Date: 10:34:00 08/23/00
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On August 23, 2000 at 12:27:39, Ernst A. Heinz wrote:
>Hi Christophe,
>
>>I have never understood this "not re-search in the last plies" trick. Obviously
>>it does not work for the reasons you have given, but I think it also simply
>>does
>>not work if you use a QSearch. I suspect this optimization works only when you
>>do not have a QSearch, and you consider the nodes at the horizon to be terminal
>>nodes. Because in this case the score you have got with the null window cannot
>>change after the re-search with the full window.
>>
>>If somebody understands it in a different way, I'm interested to hear about the
>>explanation...
>
>The "trick" has nothing to do with quiescence search which actually
>is an expensive (non-static) evaluation function.
Yes it does, Ernst. You cannot consider the QSearch to be a "black box" in this
case, because the tree searched by the QSearch, and the result it yields,
actually depends on the value of alpha and beta.
So QSearching with a full window will in some cases give a different result than
QSearching with the null window.
> That is why I use
>the general abstraction "horizon_score" for it in my book.
I agree that this abstraction can be useful sometimes, but in this case I think
you cannot use it.
>The negascout "trick" only works for _real_ fixed-depth searches
>_without_ any depth extensions and reductions. As soon as you do
>varibale-depth searches with only nominally fixed depths, the
>research is always compulsory and the negascout "trick" does not
>work because the path lengths below the node in question may be
>much longer than 3 plies until they finally reach the horizon.
And you can consider the QSearch to be a variable depth search...
Christophe
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