Author: Nagendra Singh Tomar
Date: 16:38:58 10/22/02
Hi All,
Following is the snippet of the classical PVS code
/* zero windo search */
value = -PrincipalVariation(pos, -alpha-1, -alpha, depth);
/*if the zero win search fails-high do a research */
if(value > alpha && value < beta) <=====
{
/* do a wide window search here */
}
My question is regarding line marked <=====
Should'nt the check be (value >= alpha && value < beta)
^
This is because the BETA value in the zero window call is -alpha and inside that
call it will fail-high if score >= beta i.e score >= -alpha
So a return value of -alpha from the zero window call also signifies a fail
high. So we should do a re-search for this also.
Is that OK.
Another question is that if the wide window search fails-low due to transref
tables or some window dependent extensions, what do we normally do. Do we do a
re-search with a still wider window or do we ignore the fail-low. I remember
from some Bob's post that we ignore it.
What if this condition (fail-high followed by a fail-low) occurs at the root (in
aspiration search). How can we ignore it there ?
regds
tomar
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