Author: Robert Hyatt
Date: 02:10:37 08/03/98
Go up one level in this thread
On August 03, 1998 at 04:10:34, Guido Schimmels wrote:
>Getting a fail-low at the root is annoying, as we don't know what move to play
>for quite a while.
>There is in article by Schaeffer et al. ("Advances in alpha-beta searching")
>suggesting to restart the search in these cases (setting depth to 1 again),
>exploiting the benefits of a hash-table and finding a new best-move quickly.
>But nobody seems to use this, why ? (or am I wrong here ?).
>An important implementation detail not mentioned in this paper is, how to do the
>windowing up to the search depth we restarted from - if we do aspiration as
>normal isn't there a danger to get caught in an eternal restarting-loop ?
>
>- Guido -
I haven't seen this, but don't see how it would work. Because it took
the search reaching depth D to fail low in the first case. So all that
will happen on the re-search from depth=1 is that you will fail low, then
reduce alpha to -infinity and search again. But now the hash entry that
says "fail low" can't be used, so you fail high or else get a valid score
that is back in the vicinity that it was when this mess started. If you
have to reach depth=D to fail low, searching any more at depth D-1 will
not work, because it won't understand the position (won't have enough
depth or extensions) to find the reason for the fail low.
So there could be a danger in looping, but in reality, there is a danger
of just wasting time, rather than trying to find a better move to replace
the one that failed low...
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