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Subject: Alpha beta fail soft, pruning & hash bounds?

Author: Steve Maughan

Date: 03:50:45 12/14/00

My program doesn't use fail soft atr the moment but I have been reading about it
on the web.  I hadn't realised that with fail soft the score, if less than
alpha, is an upper bound and if greater than beta is a lower bound.  I can see
that this would be useful - but how useful is it in practice?

A couple of things I can think of doing if this is the case:

1) Back up the hash score with the returned value as the bound and NOT alpha or
beta.  This would give more hash cutoffs but is it accurate when one has null
move & futility pruning etc?

2) Use the score as a better bound for a fail high - obvious but I can't see
anyone doing it.  As an example Shredder 5 seems to fail high at +0.25 above
current score then +0.50 above current score.  Surely if this fail soft property
is robust there must be a better way.

Are all of these insights correct?


Steve Maughan

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