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Subject: Re: Fail-soft with PVS?

Author: Bruce Moreland

Date: 13:26:39 03/09/99

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On March 09, 1999 at 16:17:24, Dan Homan wrote:

>On March 09, 1999 at 14:34:49, Will Singleton wrote:
>
>>
>>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
>
>I've gone back and forth on this issue myself.  My testing seems to show
>that a small window (+,- 1/4 pawn) is slightly (a couple of percent)
>faster when measured over a large number of problems than (+,- mate),
>but the coding is a bit more complicated.
>
>I think I'll test this again....
>
> - Dan

I ran with a +- 32767 window for months and didn't notice.

bruce



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