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Subject: Re: Changing alpha / beta based upon hash?

Author: Steve Maughan

Date: 01:05:41 01/02/01

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Bob,

>Those occur when I get and EXACT hit.  I search no deeper, store the table
>value as the best score here, and then stuff the PV with the moves from the
>root to the previous ply.  I then set the <HT> flag since the PV should
>have more moves, but I don't store PVs in the hash entry (this is doable
>but expensive in terms of memory).

Yes of course I do the same.

>It has to be a bug.  The most common problem is backing up a garbage PV when a
>node fails _low_ as there can be no best move, much less a PV.  If you fail
>high, you also have no PV, only a best move at _this_ ply. But the ply below
>this one is a fail low with no best move of any kind...
>
>Hashing is the special case... if you get a hit, you have to fake up a PV
>since there is going to be no further searching to back one up.  It is up
>to your hash lookup/hit code to recognize this and build a PV from each move
>played up to the previous ply...

I'll try and hunt the bug down.  I'm still not convinced but I have to do some
more experimentation.

Thanks again,

Steve



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