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Subject: Re: programmers: pawn hash tables

Author: Robert Hyatt

Date: 22:14:12 03/08/03

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On March 09, 2003 at 00:35:49, Uri Blass wrote:

>On March 08, 2003 at 23:34:35, Robert Hyatt wrote:
>
>>On March 08, 2003 at 12:05:59, Russell Reagan wrote:
>>
>>>On March 08, 2003 at 09:41:18, Robert Hyatt wrote:
>>>
>>>>Sure you can.  You can evaluate all the pawn-only stuff, and then you can
>>>>pre-cmpute whatever you need such as passed pawn locations, weak pawn locations,
>>>>weak square locations, open file locations, half-open-file locations, and so
>>>>forth.  You stuff that in the pawn hash table, and then use it when you evaluate
>>>>pieces to get the "coordination".
>>>
>>>I wonder if it would be faster (or reasonable) to keep track of this stuff
>>>incrementally. For example, from the starting position, you know that if a pawn
>>>makes a capture, or is captured, then that file is half open. So you can keep
>>>track of how many captures have been made to or from a file, and keep track of
>>>isolated pawns that way. I guess using a pawn hash would still be faster or more
>>>generally useful, and as with all things incrementally updated, you do some
>>>wasted updating computations where you may not use it.
>>
>>
>>This is a tough thing to figure out.  IE incremental updates cost something.
>>You hope it costs less than computing from scratch, which it generally does if
>>done well.  But if you start to search pretty deeply, then the payoff drops
>>off quickly, as you keep re-updating the incremental stuff multiple times
>>before you use it once when you reach the tips.
>
>1)It is the case only if you do not evaluate every node and there are programs
>that do it
>Rebel does it and movei also does it.
>
>Rebel does not do incremental evaluation but the reason is not that it is
>impossible to do it but the fact that Ed found it difficult to do it without
>bugs.
>
>2)The original question was about comparing incremental updating to pawn hash
>tables.
>I assume that for pawn structure, hash tables are faster because you may get
>almost 100% hits.
>
>Uri

Yep.  Even with a hash size of _one_, you can get decent results, because
the same pawn structure happens in successive positions many times.




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