Author: Amir Ban
Date: 15:07:00 11/24/98
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On November 24, 1998 at 10:59:13, Ernst A. Heinz wrote: >On November 24, 1998 at 09:59:02, Amir Ban wrote: >> >> [...] >> >> Junior is more aggressively extended than most PC programs, and therefore >> more than DB. > >Amir, > >I do not think that your above chain of reasoning is valid because we really >do not know how much "DB" extends. I am convinced that "DB" extends far more >than most PC programs as well. Whether "Junior" exceeds "DB" in this respect >is open to speculation but not to conclusive argument. > >BTW, I happen to remember a post on RGCC shortly before the Kasparov rematch. >The poster had apparently talked to Murray Campbell during a conference and >reported that Murray said something about the search trees of "DB" being very >broad at the top, then stringy because heavily extended in the middle, and >quite bushy again at the bottom where the special-purpose chess processors >resorted to 4 plies or 5 plies of non-selective (i.e. also non-extended?) >full-width search again. Especially the final full-width part of the chess >processors would result in a completely different tree-structure than those of >all others if my memory serves me right and the original report was true. > >=Ernst= I don't really believe this. First, because Murray is likely to have said the tree is "heavily extended" if what they did was not more than check and recapture extensions. As every programmer knows, that's already heavy, but every does it, and for Junior that's really only the beginning. I doubt Murray meant "in comparison to other chess programs", because his audience would not care about that, and as a Deep Blue team member he probably didn't care either. Second, because it does not make sense for Deep Blue to take an avant-garde position on this. Their greatest asset was raw computational ability, they had NPS to spare, and they had every reason to take a conservative position on the search and not risk their advantage. This has been said by several people before to explain some things they did, like for example SE, which other developers didn't find worthwhile, but when you start with a 100 to 1 computing advantage over your opponent may be worth just for the slight extra insurance. According to all appearances, they did in fact take this conservative approach, and perhaps even carried it too far. Hsu's prejudice against forward pruning is just that, a prejudice, which cost them expensively in computing power, but they didn't feel the heat and could indulge themselves. Against equal hardware, they would quickly forget this prejudice like all of us. Another way of saying this is that the search algorithms of Junior arose not so much because I wanted to do them in any theoretical sense, but because of the need to be competitive against opponents who seemed to outperform me. I can't imagine anyone who doesn't feel this kind of pressure doing the same, and from their point of view, doing this would probably appear irresponsible. Amir
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