Author: Ernst A. Heinz
Date: 13:08:10 01/27/99
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On January 27, 1999 at 15:48:16, Robert Hyatt wrote: >On January 27, 1999 at 15:16:44, Ernst A. Heinz wrote: > >>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= > > >Then I don't like the terms... at all... what I do is _not_ pruning in any >sense of the word, any more than null-move is direct pruning. I reduce the >depth, but I don't throw anything away in the 'razoring' code. > >OTOH, in my q-search I _do_ prune, and I have called this 'futility pruning' >because if my current material score is say -9.00, and I am about to try a >move that captures a pawn, I call that 'futile' and don't even search it, since >one pawn gain, plus the positional score, is _not_ going to pop the score back >over alpha so that it can be useful. > >I have _always_ called 'pruning' the decision to toss out a move apriori with >no searching of any kind, even to reduced depth. And the term 'futility >pruning' as I described it above has been used since the middle 70's in >discussions I have had with others. If it was used differently in a paper >somewhere, that's ok by me. But I'm not going to call the 'razoring' Idea I >use 'futility pruning' when I don't prune anything. And I'm not going to call >my quiescence pruning 'razoring' when I do prune something. :) > >Perhaps just a gross terminology issue, but the definition of 'pruning' ought >to be pretty standard. Pruning means "in the world of trees, such as my >crepe myrtles, "cutting away a branch in its entirety", not "cutting a chunk >out of a branch and sticking the pieces back together with a chunk in the middle >missing. > >Somewhere along the line, that 'pruning' term got misused, and maybe it stuck >in some cases. But the 'meaning' seems clear to me... and this is nothing more >than _really_ confusing... :) Where and why did the term "pruning" get misused in your opinion? 1. Normal futility pruning (as coined by Jonathan in his Ph.D.thesis), 2. extended futility pruning (as coined by me in the ICCA Journal), and 3. futility pruning in the quiescence search (as done by almost anybody) all *cut* (or prune if you like) moves at the nodes where they are applied according to my above explanation. =Ernst=
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