Author: Pham Minh Tri
Date: 18:58:04 08/30/01
Hi Bob,
I am studying how Crafty closes the search window in the root search (file
searchr.c). I have learned much from your code. Thanks.
There is a point I am unclear: updating beta. I am afraid that the search of
next moves may be faulty after updating it.
Suppose a situation: original value of beta = 1000, a good move brings a value
of 200, so Crafty changes beta to value+40 = 240. The next move gives a better
value of 300. Crafty says the search is good and need not re-search with wider
window and then stop searching because of value>beta. It turns out there is no
bestmove. However, if program does not update beta (beta==1000), the search has
to redo and may find a bestmove (say, a move gives exactly 400).
What do I miss here?
Many thanks,
Pham
PS: Here is pseudo code after searching with window [-alpha-1, -alpha]. I marked
the unclear points by arrows.
Search with window [-alpha-1, -alpha]
==> if ((value > alpha) && (value < beta)) {
Re-search with window [-beta, -alpha]
}
if (value > alpha) {
root_value=alpha;
if(value >= beta) {
Update some thing
return value;
}
alpha=value;
==> beta=value+40;
root_beta=beta;
}
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