Author: Amir Ban
Date: 09:09:33 11/16/98
Go up one level in this thread
On November 16, 1998 at 10:17:03, Robert Hyatt wrote: >On November 16, 1998 at 09:55:46, Amir Ban wrote: > >>On November 16, 1998 at 02:13:01, Ed Schröder wrote: >> >> >>>>Yes, you got it right. >>> >>>>The PV for Deep-Blue on all iterations except the last starts 36.Qb6 Qe7 >>>>37.axb5 Rab8 38.Qxa6 e4 39.Bxe4 Qe5. In the last iteration, there's no PV. >>> >>>Thanks for posting the main variation. I clearly remember the end position >>>again. Based on this impressive main variation I can come to no other >>>conclusion other then that Deep Blue must have a speculative king safety. >>> >> >>I'm not ruling this out as an hypothesis, but please tell me: How does a >>speculative king safety agree with moves such as g5 in the 1st game, b4 in the >>4th game, and a generally solid style throughout the match ? >> >> > >two choices: (1) in that game, I believe that even Kasparov said that g5 >was the only real possibility to consider there. At least one other GM said >this during the match as well. I don't recall exactly why they thought this >was necessary, but some did. (2) it is not difficult to have a king safety >evaluator that will suggest g5 there. I've done it *many* times although I >generally consider it a "bug" in such positions and try to tune it out. But >in doing so I would *only* be looking at the king-safety issue and the gash >in my kingside pawns that g5 produced. But if there are other deep issues >here, and some suggested they were, then g5 isn't so mysterious. We ought to >run some deep searches to see how different programs evaluate g5 and whether >they would play it, or how close it is on score to the move they would prefer >instead (if they won't play it.) > > > > >>>The other explanation, a bug, sounds not fair to the Deep Blue team. >>> >> >>Actually bugs, or general malfunction during this part of the game, is quite >>high in my list of possible explanations. There are a lot of strange things >>going on. Here's one of them (the PV for iteration 10): >> >>36. Qb6 Rab8 37. axb5 Rab8 38. Qxa6 e4 39. Bxe4 Qe5 40. Bf3 Rd8 41. Qa7 Qxc3 42. >>Bh5 >> >>Question: how to explain the appearance of the move 41.Qa7 in the PV ? >> >>Amir > >I believe they have answered this already. So did I. Nothing new in this debate ... They have problems in getting a PV >back from the "hardware" as I understood it a good while back. IE we use an >array to back up the PV when we back up a score. They can't do this, because >the hardware doesn't work like that, and there are multiple chess processors >for each SP processor, making this impossible to handle since the processors >can't communicate with each other. As a result, I believe that they use the >hash table to construct the PV after the search, since the hardware can't >push the PV back to the SP processors. And doing this, you can definitely get >bizarre PV's. I played with mtd(f) a year or so ago, and tried to do this to >construct a PV since *every* move fails high or low and my PV code was not going >to *ever* return a PV. And when I did this, I got some "interesting" stuff >back, which was one of the reasons I gave up on the idea. I believe others have >tried doing this (PV reconstruction by probing the hash table) and found the >occasional "oddball" move on the end... I "extend" my PV when I get a hash hit >by going to the end of the PV, and probing to get the best move, then making >that (if legal) and probing to get the next move, and so forth. And I have, on >rare occasions, gotten something odd. If you check my "ponder" code you will >notice that I check the 2nd PV move for legality, because it might have come >from the hash table, once every now and then it would be illegal. ANd when >I "made" it it tore hell out of my data structures and resulted in a lost game >(flag) on ICC. > I don't think so. This one is not a "nonsense" PV. It's genuine and needs an explanation. Amir
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