Author: Ernst A. Heinz
Date: 12:16:44 01/27/99
Go up one level in this thread
On January 27, 1999 at 13:54:07, Peter McKenzie wrote:
>
>Bob, what you describe as razoring (which is also what I thought was razoring
>and I haven't even read the crafty sources :) matches the definition of Futility
>Pruning as given by Ernst Heinz in his recent ICCA article (also on the
>excellent web page http://wwwipd.ira.uka.de/Tichy/DarkThought/).
>
>I guess they call it 'pruning' because, by jumping to the q-srch one ply
>earlier, you are tossing out moves that you would have searched had you not
>jumped to the q-srch.
>
>I'm still unsure of exactly what Ernst's (and others who share his definition of
> Futility Pruning) definition of razoring is. Maybe its when you just return
>alpha instead of jumping to the q-srch?
No.
I have meanwhile reread the whole thread and think to know where the
general confusion stems from (see explanation below).
1. Your and Bob's definition of razoring implies a depth reduction of 1 ply
at the frontier (remaining depth = 1 ply) with a direct jump into the
quiescence search. However, you do *not* cut any moves at frontier nodes.
2. The original definition of razoring as given by Birmingham and Kent in
1977 (as correctly quoted by Peter Fendrich) *cuts* *all* moves at
frontier nodes with static evaluations <= alpha. Birmingham and Kent
proposed even more risky stuff called "deep razoring" and "enhanced
razoring" which performed the cuts anywhere in the search tree which
featured maximal depths of 5 plies in their times. Marginal forward
pruning as suggested by Slagle is similar and at least equally risky.
3. Normal futility pruning *cuts* all futile moves at frontier nodes and
searches the remaining non-futile captures and checks to their full
depth (1 ply). This holds accordingly for my extended futility pruning
which applies at pre-frontier nodes (remaining depth = 2 plies). On top
of these two types of futility pruning, my limited razoring adds a depth
reduction of 1 ply for very bad positions at pre-pre-frontier nodes
(remaining depth = 3 plies) and subsequently subjects them to extended
futility pruning. Thus, limited razoring *cuts* extremely futile moves
at pre-pre-frontier nodes and searches the remaining non-futile captures
and checks to a reduced depth of 2 plies.
=Ernst=
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