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

Author: Robert Hyatt

Date: 07:59:45 08/25/99

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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.

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



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