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

Author: Heiner Marxen

Date: 17:23:12 12/31/00

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On December 31, 2000 at 19:36:05, Steve Maughan wrote:

>Heiner,
>
>>OTOH, a general assumption underlying all this searching business is
>>that deeper searches generally produce better (more accurate) results.
>>I.e. if we alrady have an even more correct result than the one the normal
>>search would yield, we tend to to happily accept that, and we do expect
>>to improve by this.  Right?
>
>Yes.  This is why when one raises alpha one must also cut the PV.

I do not understand the "cutting the PV" part.  Do you mean such a PV ends
with a "<HT>" TT-hit instead of more moves?

Maybe I should reread the corresponding part in Ernst's excellent book.
Maybe you should also do that ;-)

>  What is
>really happening is the deeper search info is being graphted onto the search.

Graphted?  Typo?

>>Of course you could restrict TT hits to only occur if the draft exactly
>>matches the depth.  I suspect that would reduce the benefit from the TT
>>in most cases, and quite drastically so in some cases (like the famous Fine >70).
>
>Yes I'm sure there's scope for fiddling when Depth = Hash Depth.
>
>>Do you really exclude TT entries with a larger draft?
>
>I'm not sure what you mean.

I mean:  Do you really not use the value from a TT entry if the depth
stored in the TT entry is larger than the depth demanded by the search?

>I think I'm finally started to get my head rpound this issue - it's being vexing
>me for days!!

I know that feeling!  Do not give up!
Draw some pictures.  Construct a minimal demo case.  etc

Most of the time finally I find out that things are quite simple, and the
complex part was a misunderstanding  ;-)

Cheers, and a happy new year!  (Here around it is already 2:10am)

Heiner



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