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Subject: Re: Question for the MTD(f) experts

Author: Fabien Letouzey

Date: 11:00:36 04/15/04

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On April 15, 2004 at 13:15:29, Robert Hyatt wrote:

>>>3.  PV has to be yanked from the hash table and that makes it flakey at times as
>>>has been discussed many times.  There is another way to get the PV, but it is a
>>>special case solution only for mtd...

>>Could you give me a pointer on the special way to get the PV (not with hash
>>tables)?  I'm interested in the preconditions.

>>Fabien.

>Not my idea, but it goes like this.

>On the next-to-last search, you will fail low or high.  You adjust the bound and
>search again and on the last search you fail in the opposite direction.  You cam
>catch this condition and use it to recognize the path that leads to the same
>position for both searches.

>I don't remember who came up with this, memory is suggesting Brian Richardson,
>but I'll let him speak for himself if I an correct...  He and I were playing
>with mtd(f) at the same time, he kept it, I didn't.  :)  Which certainly means
>he knows more about it than I do...

I see.  I think I suggested the same:
http://chessprogramming.org/cccsearch/ccc.php?art_id=251543
Note that one can get one more ply (then just the "agreed" line) by beeing
careful.

IMO it is not specific to MTD(f) (this is why I asked for precisions), but to
any alphabeta-based algorithm that uses segmented windows.  The same idea can be
applied to negascout for instance.  I think careless implementations of
negascout may output buggy PVs (when the "shortened window" re-search fails
low).

Fabien.




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