Author: Robert Hyatt
Date: 07:46:40 01/22/02
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On January 22, 2002 at 04:43:30, Tony Werten wrote: >On January 22, 2002 at 00:46:01, Robert Hyatt wrote: > >>On January 21, 2002 at 10:55:50, Daniel Clausen wrote: >> >>>Hi >>> >>>On January 21, 2002 at 10:41:39, Robert Hyatt wrote: >>>[snip] >>>>1. If you get a fail high at the root on a zero-width window (any move after >>>>the first move should be searched with a zero-width window) you can't trust it >>>>unless you re-search it with a bigger beta bound and make _sure_ that it doesn't >>>>then fail low. Such fail-high (zero window) fail-low (non-zero window) is an >>>>artifact of null-move and if you play such a fail high move even if it fails low >>>>on the re-search, you will die... >>> >>>Anyone has a trivial example at hand which demonstrates this behaviour? >>> >>>Why is it that a fail-high with a zero window can't be trusted but a fail-high >>>with a non-zero window can? Is "non-zero window" enough to be trusted? Or does >>>it have to be a certain minimum window? I'm sure that as soon as someone posts a >>>mini-example which shows this behaviour, even I will understand it. :) >>> >>>Sargon >> >> >>I don't have an example now as I found this bug several years ago and then >>eliminated it as I explained. It is an artifact of mixing null-move with >>the null-window PVS search. > >Did you find it to be related to the size of the window ? That's what I seem to >get from some tests. > >BTW wouldn't that make MTD quite useless ? > >Tony I think it is related to your evaluation code and search extensions. The size of the original aspiration window had no effect for me, because the problematic fail highs were _always_ on the null-window PVS search on a root move other than the first one. I found some positions where _every_ move would fail high on the null-window search then fail low on the re-search. Turning off null-move cleaned it up perfectly. Just ignoring the occasional erroneous fail-high has worked well for me...
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