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Subject: What is the advantage of fail-soft?

Author: Bas Hamstra

Date: 05:21:32 08/25/99

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?

Bas Hamstra.

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