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Subject: Re: What is the advantage of fail-soft?

Author: Inmann Werner

Date: 00:30:13 08/26/99

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On August 25, 1999 at 10:59:45, Robert Hyatt wrote:

>On August 25, 1999 at 08:21:32, Bas Hamstra wrote:
>
>>My program returns sometimes values outside (a,b), for example MATE. I believe
>>generally when you allow this, it is called "fail-soft". What is the advantage
>>of it?
>>
>>I vaguely have read somewhere that the advantage lies in better bounds
>>information. In interprete that as: you put better bound info in your hashtable.
>>Is that correct? If so, is it a factor?
>>
>>Secondly: I use simple alpha beta (not even pvs) with an aspiration window. Now
>>at some testposition it fails high at the root and score turns out to be 250.
>>New aspiration window is set (200, 300).
>>
>>Now it fails low. However: full (-inf,inf) gives 243!!
>>
>>I use no pruning at all. Could the cause be the returning of values outside
>>(a,b)? I think my basic routines are correct, including hashtable. Only thing I
>>do is strip losing captures from the qsearch.
>>
>>Last: *if* fail soft has advantages, what are the disadvantages?
>>
>>Regards,
>>Bas Hamstra.
>
>
>The advantages are minimal but do exist.
>
>1.  when you fail high or low, you have some 'estimate' of how far outside
>the window the true score will end up, so that you might choose to avoid
>setting beta to +inf or alpha to -inf, for example..
>
>2.  you get slightly better bound information stored in the hash table, so
>that there is a better chance that these bounds will be used later.
>

But isn't that risky. I thought, each score outside alpha-beta can be incorrect,
and then store it in Hashtables for bounds? Can't that give irregular things?

Werner

>3.  if you try mtd(f) it is critical to get the better 'estimate'...



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