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Subject: Re: Researching after a fail-low

Author: J. Wesley Cleveland

Date: 14:02:36 08/19/00

Go up one level in this thread


On August 18, 2000 at 19:06:03, Robert Hyatt wrote:

>On August 18, 2000 at 14:48:43, Dave Gomboc wrote:
>
>>On August 18, 2000 at 13:53:16, J. Wesley Cleveland wrote:
>>
>>>On August 18, 2000 at 09:23:38, Robert Hyatt wrote:
>>>
>>>>On August 17, 2000 at 18:05:41, Gian-Carlo Pascutto wrote:
>>>>
>>>>>On August 17, 2000 at 14:43:08, J. Wesley Cleveland wrote:
>>>>>
>>>>>>When you have a fail-low in a deep search where the value drops significantly,
>>>>>>finding an alternate move can take a very long time. This is largely because >the
>>>>>>values in the hash table are largely useless, so in effect we are researching
>>>>>>the entire tree. It seems to me one should use iterative deepening, and start
>>>>>>from ply 1 again.
>>>>>
>>>>>This technique has been described by Schaeffer a long time ago...
>>>>>
>>>>>(Obvious question: Why is nearly no-one doing it?)
>>>>>
>>>>>--
>>>>>GCP
>>>>
>>>>
>>>>I'm not sure what you mean by described a long time ago.  But there is a big
>>>>problem.  If you start over at 1 ply, you don't get the fail low score.  You
>>>>find (again) the _wrong_ move, until you get deep enough.  When there is a big
>>>>score swing between two iterations, you take your lumps.  There is no way to
>>>>cheat alpha/beta there.
>>>
>>>You should get the fail low score, since it is in the hash table. They should
>>>stay there as they are analyzed to a greater depth than you are likely to get
>>>to.
>>
>>Yes, the technique relies upon the information from the deeper searches being
>>present and used to perform cutoffs at shallower searches.
>>
>>Dave
>
>
>Doesn't this sound _gross_ time-wise?  You find another move that doesn't fail
>low, until the last iteration when the truth is found.   If you repeat this
>a few times, it seems worse than just searching for a new best move???

I thought that was what I *was* suggesting. At this point, all you know that
move a, which you thought was good, is terrible. So why not treat it as almost a
new position and research from ply one. If several lines are all going to fail
low at a deep ply, your search is in big trouble anyway.



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