20070721, 08:21  #1 
"Brian"
Jul 2007
The Netherlands
7×467 Posts 
Status of GIMPS proofs
If I've understood things  but please correct me if I'm wrong or incomplete  GIMPS aims to discover and prove three aspects of Mersenne numbers:
(1) Discover new Mersenne Primes (2) Prove that there are no lower Mersenne Primes than the ones already discovered (3) For composite Mersenne numbers with accessible factor(s) find the lowest factor (1) and (3) are clearly relatively easy to verify by the Mathematical community because they involve individual Mersenne numbers. But what about (2)? It is not really independently verifiable that what GIMPS now calls M39 is the 39th Mersenne because noone can run tens of thousands of computers for another 10 years. My question is: is there feedback, positive or negative, by independent Mathematicians about the status of GIMPS' findings about the number of Mersenne Primes in particular exponent ranges? Are the safeguards (the double checking of Lucas Lehmer tests and requirement of two tests with the same final residue) generally accepted as proof by the general Mathematical community or is there some controversy? I've seen only positive references to GIMPS on the internet by the way. 
20070726, 02:17  #2  
"Richard B. Woods"
Aug 2002
Wisconsin USA
2^{2}×3×641 Posts 
Quote:
Some earlier Mersennehunting efforts tested only certain ranges and skipped others, so were nonexhaustive. Quote:
In GIMPS, factoring has been only secondary, performed only because it was the most efficient way, up to a certain point, to eliminate candidates without performing the costly LucasLehmer computation. Early in the project, finding the lowest factor was a convenient sideeffect of this primecandidateelimination effort. It does have some mathematical value. So, the trialfactoring portion of the software, which for reasons of efficiency searches for factors somewhat outoforder (though eventually checking all possibilities), would, upon finding a factor, spend a small amount of extra time determining whether there was also a slightly smaller factor or factors that would have been found if candidates had been tried in strictly sequential order. That guaranteed that the smallest factor was found. Unfortunately, there was a software bug that sometimes caused that extra endsearch to be skipped. Once it was discovered, it meant that some earlier GIMPS factoring results were not guaranteed to be the lowest factors. It was decided to omit that extra endsearch for all efforts beyond a certain point. So, currently, factors found are not guaranteed to be the lowest. Quote:
Quote:
Quote:
Another example of what I'm calling experimental computational mathematics was the 1977 proof of the FourColor Theorem. It was done by computer program, it had the possibility of hardware or software error, and so was not _absolutely_ proven. (But as of 2005 another, independent proof seems to have been more certainly verified.) Indeed, the FourColor Theorem had a precomputer history of published "proofs" that turned out to have flaws! See the MathWorld entry at http://mathworld.wolfram.com/FourColorTheorem.html. 

20070726, 03:10  #3 
"Mike"
Aug 2002
5×7×227 Posts 
BrianE
Is the guinea pig in your avatar yours? 
20070726, 10:25  #4 
"Brian"
Jul 2007
The Netherlands
7·467 Posts 
Cheesehead thanks for your detailed reply!
OK, so (3) the lowest factor of composite Mersenne numbers is not a GIMPS goal. And I appreciate the points you make so succinctly that the goals are perfectly verifiable with increasing computer power, plus that all cutting edge Mathematics is hard to verify in any case and errors have been made throughout history. The Four Color theorem was indeed a nice example of an early (in computer history) very difficult proof carried out using brute force software attack based initially on clever Mathematics and programming. Also a good example of previous flawed attempts as I read in the link you give. I appreciate that GIMPS and other distributed computing projects are not really any different in principle, just larger scale because of widespread participation. Thanks again for your lucid help. Brian. 
20070726, 10:29  #5 
"Brian"
Jul 2007
The Netherlands
7×467 Posts 
Ah.... you've got me. No, sadly it's not my guinea pig. You've correctly identified the species, I hope you haven't identified the individual and are claiming any damages or anything.
No, I got this little guy (or girl?) from a large number of photos posted on the internet by a guinea pig breeder who I hope couldn't possibly object. Hope the guinea pig wouldn't either. I'm really hoping to preempt the habit you moderators apparently have of imposing an avatar on people  because I'd really like to use this one. Hope that's OK. 
20070727, 00:40  #6 
"Mike"
Aug 2002
5×7×227 Posts 
Guinea pigs are cool.

20070802, 21:48  #7 
6809 > 6502
"""""""""""""""""""
Aug 2003
101×103 Posts
5·7·263 Posts 

20070802, 23:15  #8 
"Mike"
Aug 2002
5·7·227 Posts 
We read they are actually a food staple for people in some countries in South America. Peru or Chile maybe?
At least if they try to run away they aren't getting very far. The few we had couldn't even jump (purposely) 23 inches. They did tend to have random seizurelike jumps that exceeded that distance but we doubt they could use that to their advantage during an escape attempt. 
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