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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