Yes, and yes. ALL log files will be useful. If everything was indeed lost, all tests for which there are no records will need to be redone. So every result from a log file is one less result that will eventually have to be repeated.Originally Posted by endless mike
First, I have several log files that I will send after the last one finishes.
Secondly, why is it necessary to redo all of the old ones? We know that all exponents below a certain limit (27,700,000) have been checked - I don't see a need to redo those.
We don't know which ones were double checked -- and at PrimeGrid I've got a really good window into the quality -- or lack thereof -- of the computers used in distributed computing. In general, we no longer trust any results unless they're double checked. The problem with not immediately double checking results is that when a computer starts going bad, you have no way of detecting it. So any results that don't have matching residues from different computers are suspect. Unless we get really lucky, except for whatever we can get from log files, we have no residues at all on 4 of the 6 k's.
Calculation errors are proportionally more likely to occur on larger candidates, especially when the error rate is fairly low, but non-zero.
Our position on double checking is especially rigid when it comes to conjectures like SoB. Consider a hypothetical k where the first prime is at n=100,000, and the second prime is at n=100,000,000. If you miss the first prime because of an undetected computation error, many years of unnecessary computing will be wasted searching for the second prime.
It's actually not as horrible as it might seem at first glance. The vast majority of candidates are small and can be rechecked much faster than the original search.
Unlike the Mersenne prime search, we only need to double check positive results. The time double-checking is better spent checking new numbers. For Mersenne primes, we want a complete list. For 17-or-bust, we only need to find a prime for each coefficient. If we get a false negative, no harm is done if we find a prime for that coefficient.
A false negative would mean a missed prime. Potentially wasted years of computing would count as harm in my book. That's the main reason I gave up on SOB and went back to GIMPS.
Yes, but the purpose of SOB is to try to prove the Sierpenski conjecture. Large primes are very rare and a false positive is extremely rare. Double-checking in SOB cuts the throughput down by half. In other words, double-checking essentially doubles the expected computing that has to be done to prove the conjecture.
Consider the highly unlikely possibility that there's only one prime for a given k. A false negative with no double checking means we crunch that k forever and never prove the conjecture. Unlikely to happen that way, but not impossible. People more in the know claim an error rate of about 4% (IIRC) on GIMPS. On the PrimeGrid message board, someone mentioned that a SOB work unit had to be sent out on average of 4.7 times to get a matching doublecheck. That post is three years old, but I can't image the situation is much different now. I still think double checking is valuable.
I will get my results files to you; might take me until Monday though. Real life responsibilities come first.
Thank you! There's no need to feel rushed. Louie can, of course, take as much time as he needs, and we're not going to rush him. We're not going to take any action until he determines if restarting SoB is possible.
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