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Subject: Re: negascout vs pvs

Author: vitor

Date: 23:42:33 06/04/99

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On June 04, 1999 at 22:08:18, Dave Gomboc wrote:

>On June 04, 1999 at 21:54:16, vitor wrote:
>>theyre basically the same except negascout has the extra depth>2 condition.
>>their performance numbers are near equal too. negascout searches maybe 0.1%
>>fewer nodes. another thing is ,if you're using extensions, doesnt it get more
>>complicated to properly detect depth>2? so is it worth it to include the extra
>PVS can be enhanced with the depth_remaining<=2 test too.  PVS and NegaScout are
>different, but this is not the difference.

what is the difference between the two?

>Using the depth_remaining<=2 early exit is bad if you use extensions.  It is a
>subtle bug, and to my knowledge, this has not been mentioned in the literature.
>Jonathan Schaeffer found this one the hard way many years ago, debugging a
>search that gave incorrect results. :-)  Considering that the complete special
>condition for early termination of the search line occurs next to never, it is
>probably faster to not do the check at all, even if you don't extend, that is,
>the depth_remaining<=2 refinement is not really worthwhile.

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