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Subject: Re: Shredder's bug?

Author: Jaime Benito de Valle Ruiz

Date: 06:23:35 12/21/03

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On December 21, 2003 at 09:05:42, Omid David Tabibi wrote:

>On December 21, 2003 at 08:53:39, Jaime Benito de Valle Ruiz wrote:
>
>>I've never read any thread about this before, so forgive me if this is a
>>recurring topic.
>>Many people have noticed that the Principal Variation shown by Shredder is
>>sometimes ridiculous, to the point of giving out its queen and a rook for
>>nothing, or allowing a silly mate.
>
>My understanding is that unlike most other engines when failing high or low
>Shredder does display a full PV extracted from hash tables (whereas other
>engines just show the first move). These moves have naturally bounded scores,
>and so are not reliable. That is also one of the main problems in extracting PV
>using MTD(f) search. But other than that, Shredder's PVs are accurate.
>

I used to retrieve the PV from the hash table... and sometimes I got "funny" PVs
as well. Maybe you're right


>
>>If this is “really” what Shredder is
>>thinking, then I’m truly surprised that it’s such a strong engine… considering
>>that it chooses absurd lines that lead to self-destruction. My engine sometimes
>>does something similar, and I’m sure it’s a bug, because the final static
>>position of the PV does not match the score is showing anyway (I have other
>>things to correct before the PV at the moment anyway), and neither does for
>>Shredder.
>>Is this a really a bug, or just a trick to conceal the way engine is doing the
>>internal search? Because I don’t believe that those PVs are the ones Shredder is
>>using for analysis, and still play decent chess.
>>What do you think?
>>
>>  Jaime Benito



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