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Subject: Fail-soft with PVS?

Author: Will Singleton

Date: 11:34:49 03/09/99



Using PVS, I can't seem to demonstrate a clear benefit to using a small window
around the root score, as opposed to +-mate.

Using a window of, for example, one-third pawn, if a move fails-high or low, it
takes fewer nodes to ascertain the move that caused the change, because you
don't have to find the real score right away.  But then you've got to resolve
the new score, and that will take more nodes since you've got to re-search with
the relaxed window.

And if, after a fail-high or low, you attempt to delay score resolution until
the next ply (to avoid the re-search at the same ply), it seems you might have
the problem of finding a worse move after the fail at the same ply, since you
don't know the real score yet.  This would result in even more nodes being used.

So I don't see much benefit, unless I'm doing something wrong (likely).  On a
normal search, without any fails, I see either more or less nodes (between
windowing and +-mate), depending on the position.  But not really much change.

Any comment would be apppreciated.

Will



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