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Subject: Re: Deep Search Extension

Author: Robert Hyatt

Date: 08:26:02 01/22/98

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On January 22, 1998 at 09:01:59, Ernst A. Heinz wrote:

>On January 22, 1998 at 08:42:06, Robert Hyatt wrote:
>
>>Yep... Forgot.  For me, I couldn't do the above... because I don't use
>>fail-soft and most scores (excepting mate and draw) are always inside
>>the alpha/beta window.  But shifting the null-move window down does
>>exactly the same thing, ie searching alpha-piece, beta-piece produces
>>the same information.
>
>Yes, but it is much more expensive because you must do a second null
>move search whose trans/ref efficiency is probably bad because of the
>shifted search bounds. Furthermore, the condition of the static
>evaluation failing high is important.


actually it is not that expensive, because it is hardly ever done.  Only
when backing up a score that is not alpha (meaning this is either going
to
fail high unexpectedly or else this is a true PV search.)  The null move
wasn't the real killer for me at all, because I used to have code to
measure
how much extra searching I did.  The killer was extending moves that
really
didn't do anything good for the search, except burn CPU time...

>
>>I thought my idea of first noting that this was a PV move, and then
>>trying the null-move threat extension only after that was from the
>>paper.
>
>As you can only do a non-zero window null move search somewhere down
>the PV, this is certainly implied by the paper.
>
>=Ernst=



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