20191208, 01:28  #254 
Feb 2005
Colorado
2·3·7·13 Posts 
With quadrillions upon quadrillions (that is a huge understatement actually) of possible ECM curves that could be run, do you have an alternative to random when it comes to picking which one to run?

20191208, 14:26  #255 
Random Account
Aug 2009
U.S.A.
694_{16} Posts 
No, I do not. I wish there was another way. A lot of people spent a lot of time running ECM's on M1277. In the end, everyone had to surrender. At the time, I remember someone writing, "A factor will be found using SNFS." If a person takes it out into decimal form, it is 385 digits long, if I remember correctly. As far as I know, none of the YAFU functions can handle something that large. As the same time, other programs would say this is too small. All of us will simply have to carry on with what is available now.

20191208, 16:22  #256  
Feb 2005
Colorado
2×3×7×13 Posts 
Quote:
It is easy to lose perspective of how large the numbers we are dealing with really are. We talk about a 385 digit number like it is just a number, when the total number of atoms in the entire universe is only 70 or 80 digits. That puts it somewhere between ten quadrillion vigintillion and onehundred thousand quadrillion vigintillion No, I have never heard of a vigintillion until now either. 

20191208, 18:05  #257  
"Curtis"
Feb 2005
Riverside, CA
3^{2}·7·71 Posts 
Quote:
Some very rough numbers: Let's say we've done t73 worth of ECM. The nth digit worth of ECM has a 1/n chance to find a factor, so going from 73 digits to 80 digits has, say, 89% chance to find a factor. Before we get to t80 worth of ECM, someone will more precisely calculate the "right" amount of ECM to do. The SNFS job itself can be run with current software (and a cluster to solve the matrix); it is perhaps 48x tougher than RSA240, the largest GNFS job known to be solved. 

20191209, 00:56  #258 
Random Account
Aug 2009
U.S.A.
2^{2}×421 Posts 

20191209, 01:25  #259 
"Curtis"
Feb 2005
Riverside, CA
3^{2}×7×71 Posts 
Tnn = digit level to which ECM has been performed. e.g. T50 is shorthand for saying the standard number of curves have been performed at the 50digit level (B1 = 43M, with the exact number of curves depending on B2 choice).
There are conversions available to convert from other B1 choices, usually via the GMPECM v flag, which tells you how many curves at your chosen B1/B2 it would take to complete T50 or T55 or whatever. Common use is to only report in 5digit increments, e.g. T65 or T70; I used T73 as a nonstandard way to say "half a T75", while also saying that we've run enough curves to expect to find 71 or 72 digit factors (with "expect" far from "sure we would have found"). Speaking in generalities, it takes about 6x as much work to complete the 5digithigher Tlevel. So, T50 is about 6x longer than T45, likewise T80 is about 6x longer than T75. Edit: as for surrender, Ryan does more work than the rest of us put together; primenet showing a slowdown may just mean he moved on to other candidates. I interpret "surrender" as "gave up", while the reality is that many folks remain interested and may continue ECM in 2020. Edit2: I typo'ed, and should have said T73 expects to find factors 73 digits or smaller. That is, after a T70 has been completed, one would expect that half a T75 would find "most" 71 72 73 digit factors (as well as nearly any <71 digit factors that the T70 missed). Last fiddled with by VBCurtis on 20191209 at 01:33 
20191209, 14:03  #260  
Random Account
Aug 2009
U.S.A.
3224_{8} Posts 
Quote:
M1277 was factored to 2^67, I believe. None of the current programs will run an exponent this small, except for Prime95 and GMPECM. Prime95 says to run ECM. Someone in the past ran a huge P1 test. The lower bound was 13 digits long. 

20191210, 10:30  #261 
Romulan Interpreter
Jun 2011
Thailand
2^{2}·7·11·29 Posts 

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