Author: Amir Ban
Date: 06:56:15 04/20/98
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On April 19, 1998 at 19:33:25, Fernando Villegas wrote: >Hi Amir: >I have just played my first game against Junior -the module in Fritz- at >a relatively serious rhythm, 40 in 60, game that I lost after 50 moves >of a very hard fight for him but specially for me, of course, otherwise >I would be the winner. >My first impression is that the expression “fast searcher” with which is >defined even by you in the cd-rom clip is somewhat misleading as much as >there is some ambiguity in the definition of what it is “fast” search in >the first place. >What I saw is that Junior reaches very very soon 12 ply, faster than >Fritz even if Fritz counts more nodes per second than Junior. Then, I >thought that the speed of search should not be automatically considered >like something equal to the count number, but to the ply number. In my >opinion Junior is fast because he goes very soon to very deep searches, >not because the great crunching of nodes he does to get that. I can >easily imagine an even faster computer in terms of nodes, but very slow >in terms of ply if the search is totally full-width, without any pruning >at all. In that case the very fact of exponential growing of the tree >would impede a deep search at all. On the contrary. I can imagine an >slow thinking machine -like the human brain- reaching very deep levels >of ply because of an exceedingly good pruning or selective search. >So, when we say that this or that program is “fast searcher” we are not >concluding the search of how that program is, as it seem to happens, but >just beginning with it. We don’t advance even an step saying that a >program is “fast” searcher in comparison with another that supposedly is >“knowledge searcher”. If, as I think, fast search equals deep search, >then there is a pruning device, a selective criteria. And if there is >such thing, the key to understand the problem is not just to say how >“fast” the program is, but to insvestigate how the program do so deep >search. >So, dear Amir, why don’t you tell us a little bit the way you get those >very deep searches? >Fernando Hmmm ... I thought at least you, of all people, would remember the CCR article you did on Junior. It should have answered that question at least. Everyone is complaining that the programmers are not talking, but the truth is that when they talk, nobody listens. I guess that's how they learned to shut up :) I think your question is more likely to be asked by a non-programmer than a programmer. The Junior depth value measures half-plies, so if you insist, it's ply 6. I could have called it ply 12 or ply 9 with equal justification. Since nobody does brute-force anymore, and everybody does both pruning and extensions, what the depth indicator means is a bit vague. Very roughly, I would propose this equality: Genius depth 6 = Rebel depth 8 = Fritz5 depth 10 = Junior depth 12 which once said should be forgotten, since it's much more complicated than that. Deep searches ... Junior's lines often come very deep quite soon. It's impressive, I know, but there is nothing intentional about it. It's a result of search heuristics that have no special preference for "deep". The real points about this are usually missed: 1. The quality of the search is as good as it's weakest part. It's no good analyzing your PV's to 30 ply if you are likely to fall for an odd 3-mover you overlooked. 2. Most programs can extend lines to wild lengths, and actually do in the search, but these lines don't often turn up in the PV. In Junior, they very often do, so you get to see them on the screen. Junior, being an alpha-beta program, doesn't know in advance that a line it's looking at will become the PV, so the fact that PV's tend to be long is an indication that the search heuristics are doing something right, that is, they follow what is indeed important in a position. Amir
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