20050629, 07:06  #1 
Jun 2005
576_{8} Posts 
I don't understand. I thought the purpose of P1 factoring was to weed out exponents with smaller factors, thereby eliminating the need for some lengthy LL tests. If it's already been LL tested, what's the point of P1 factoring?
Last fiddled with by drew on 20050629 at 07:12 
20050629, 09:27  #2 
Oct 2003
Australia, Brisbane
2×5×47 Posts 
(My appologies for moving your thread. It was just that I would prefer to keep blocks of work from having posts in them that don't specifically relate to that block of work. Please feel free to start new threads though.)
These exponents have only been LL tested once. Before we can verify that an exponent is not prime, we (GIMPS) must have 2 matching residues. This is due to the fact that about 1.6% of all LL tests are bad. (I think that it is 1.6% of all LL tests, or it could be 1.6% of LL tests with a 00000000 error code) Therefore, each exponent has to be double checked. We go ahead of the leading edge of double checking doing further factoring on these numbers to see if we can find a factor. If we can, we eliminate the need for the lengthy LL double check. Also, if the original test (or the double check) was wrong, we have also eliminated the need for a triple check. Also, making a sweeping generalisation here, the majority of computer assigned to doublechecking are older, slower computers. These older computers don't usually have the required RAM to run a p1 test, so once again it will be skipped (or simply won't run stage 2). Therefore, we at mersennearies try to p1 all these exponents before they go to primenet for doublechecking. I don't have up to date numbers, but off all the exponents that i have p1ed, I find a factor about 4.5% of the time. That is ALOT of p90 hours saved. Ideally, it would have been better if these exponents were p1ed BEFORE their first LL test, rather than after like we do, but at the end of the day, a factor is a factor. edit to include some stats According to James Heinrich's stats site... I have spent 56.5 p90 hours p1ing I have saved 331.8 p90 hours Therefore, I have saved a net of about 275 p90 hours by p1ing with mersennearies Last fiddled with by dave_0273 on 20050629 at 09:35 
20050629, 15:00  #3  
Jun 2005
2·191 Posts 
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