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Subject: Re: Building the Principal Variation in MTD(f) searches

Author: Vincent Diepeveen

Date: 13:06:49 07/19/99

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On July 19, 1999 at 13:41:37, Dave Gomboc wrote:

>On July 19, 1999 at 06:14:45, Vincent Diepeveen wrote:
>
>>On July 19, 1999 at 00:14:28, Dave Gomboc wrote:
>>
>>>On July 18, 1999 at 21:11:20, Vincent Diepeveen wrote:
>>>
>
>[snip]
>
>>>>That's not true, as in the worst case your window is a pawn off.
>>>>So the first 5 researches are searching space which is completely useless,
>>>>where in PVS the search overhead only depends upon move ordering.
>>>
>>>The more useless the search, the quicker it terminates.  If you're a pawn off, a
>>>cutoff should be extremely quick.  Searches that are close to the proper value
>>>take longer, precisely because they are searching space that is not "completely
>>>useless", as you put it.  And that effort will be caught in the hash table, so
>>>you don't have to search it twice.
>>
>>That's not entirely true.
>>
>>a) it's overhead which PVS doesn't search
>
>mtd(f) searches minimal trees to prove what it needs to prove.  PVS also has a
>lot of overhead that mtd(f) doesn't search.

You really eat that?

>>b) you do not get it from hashtable as you search with a way lower bound
>>   next iteration, and then another lower research, where nullmove
>>   has the habit to give for alfa and beta scores back which are simply
>>   equal to alfa and beta. So you do need to research and can't
>>   use hashtable cheap

>When the score doesn't move far, a ton of the re-search is in the hash table.
>When it does, the first search didn't take very long anyway.

Please reread what i wrote. Your assumption is not true. Score is namely
far of.

>[snip]
>
>Dave



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