Author: Christophe Theron
Date: 00:57:00 08/23/00
Go up one level in this thread
On August 23, 2000 at 03:42:09, Dieter Buerssner wrote:
>On August 22, 2000 at 21:57:58, Antonio Dieguez wrote:
>
>>can a kind person explain me Negascout?
>>what it does in addition of pvsing?
>
>I think there are two differences between Negascout and PVS.
>
>Both use zero window searches with -alpha-1, -alpha for the recursive call.
>If the score returned from the recursive call is > alpha and < beta, Negascout
>will research with -beta, -score while PVS will research with -beta, -alpha.
This is a subtle difference and actually one should try both versions and see
which one works better.
>Also Negascout will not research, when the depth is the final depth - 1 or
>the final depth - 2.
>
>I believe, this last point won't work, when you have pruning decisons in
>qsearch,
>that depend on the window (i.e. you skip capturing moves, that look, as if they
>could not bring back the score to alpha), or when you use futility pruning close
>to the leaves of the tree.
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...
Christophe
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