Author: Robert Hyatt
Date: 05:22:03 01/20/00
Go up one level in this thread
On January 20, 2000 at 03:22:56, Jeremiah Penery wrote: >On January 20, 2000 at 02:18:51, Ed Schröder wrote: > >>On January 19, 2000 at 18:55:42, Dann Corbit wrote: >> >>>On January 19, 2000 at 18:34:52, blass uri wrote: >>>[snip] >>>>The question is if the move of deeper blue was the right move. >>>>It is not clear that 36.axb5 was the right move. >> >>>So the argument against 36.axb5 was that it is not such a good move? >>>Every program has bugs. There are a very large number of tunable parameters >>>with the deep blue machine. Perhaps one (or many) of them was not optimal. >> >>You misunderstand. It's the DB main-line for 36.axb5 what made Kasparov >>suspicious. In this main-line DB sacrificed 3 pawns for no direct win >>but for a dangerous looking king attack, all very human-like. Kasparov >>could not believe his eyes (he still can't) and started the accusation >>human intervertion took place as he could not believe a computer was >>able to produce such a (super) main-line. >> >>So this whole issue is NOT about the move 36.axb5 but about the asthonising >>main-line DB produced. > >I think it depends completely on the evaluation, specifically the king-safety >evaluation. From looking at the log files, it seems that DB evaluated >king-safety much differently than most (all?) other computers. [I could be >wrong here - I'm basing this by the fact that the last move of many of the PVs >it gives were strange looking moves that seem to lose material to open lines on >one of the kings, like in this PV from move 37 of game 2: Be4 Rcb8 g3 Qd8 Ra6 >Rxa6 Rxa6 Bc7 Rxf6.] It may also have been asymmetrical, valuing its own >king-safety higher than the opponent's. >Certain modified Crafties I've produced will play axb5. Some of them will play >it right away, and some will switch from Qb6 after a deep search. One in >particular I remember liked Qb6 for a long time (15 ply, IIRC), then produced a >line _very_ similar to the one DB produced for that move. It switched to axb5 >before the next ply, just as DB did. > >I think I'll go back and analyze again the line DB gave for move 36. Qb6, to see >if white could get improve on it and get better than a draw. > >Jeremiah The PV of DB is totally unreliable. Remember this: When they did what they called an 11 ply search, that was 11 plies in software, plus another 4 plies in hardware, plus captures. And also recall that the hardware only returned a score/best move... there was no facility to try to store the PV in hardware (Belle had the same problem). Which means that the only way to construct a PV is to probe the hash table. You would think that this is totally accurate, but it isn't. In Crafty, when I get ready to do a ponder search, I try three things: 1. If I have a PV, and it contains 2 or more moves, I try the second move in the PV. 2. If 1 fails, I do a hash probe and if I hit, _and_ the entry has a move (all entries don't have a best move, ie positions that failed low) I try that move to ponder. 3. I do a search for the opponent (short time limit) if 1 and 2 fail. I see, fairly frequently, where I fail high at the last minute, which means that I have no PV. So (1) above fails. (2) gets a hit and I ponder some move where the score is +7.xx, even though the real score is only +1. The opponent makes a more reasonable move, and the score drops back to +1 or so. If I produced a PV with that move in it, it would look ridiculous. Since DB's hardware can't back up a PV from the hardware, the hash table is the _only_ place you can pick this up. And the deeper you go, the farther you get from reality. The end of the PVs can be utter nonsense...
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