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Subject: Re: Zero-width Window Null Move Search

Author: Roberto Waldteufel

Date: 10:35:02 06/22/98

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Hi Guido,

It seems I had misinterpreted Negascaout. Perhaps my misinterpretation even
constitutes a new variant of this family of search algorithms. My metod on each
iteration is as follows:

At each node, I search the first move with window {alpha,beta):

value=-Search(-beta,-alpha,depth-1)
If value>alpha then
   If value>=beta then
      Search=value
       Exit
    End If
    Alpha=value
End if



Then, if I did not get a beta cut-off, for each subsequent move from that node I
do a null width search, with a research if necessary,like this

value=-Search(-alpha-1,-alpha,depth-1)
If (value>alpha) and (value<beta) then
   value=Search(-value,beta,depth-1)
End if

If value>alpha then
   If value>=beta then
      Search=value
       Exit
    End If
    Alpha=value
End if

This was my interpretation (or misinterpretation) of Reinfeld's pseudo-code. To
be more precise, I search to depth instead of depth-1 if the side to move is in
check. Compared to classical alpha beta with infinite window, it was a great
improvement. I'll have to look at Reinfeld's code again a bit more closely, but
my method seems to work so well that I would need to be really convinced before
recoding it all over again. Do you think I could improve my speed with a proper
PVS? Maybe I waste a lot of time searching the first move to full width instead
of with a null window.

Best Wishes,

Roberto



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