20050311, 00:33  #12 
Sep 2002
Oeiras, Portugal
2^{3}·181 Posts 
You´re right. The LL test shouldn´t use more than 1214 Mb of memory. If less than the minimum memory is allowed, the program just skips stage 2 and goes straight to the LL test.

20050311, 12:11  #13  
Jul 2004
Potsdam, Germany
3·277 Posts 
Quote:


20050311, 14:31  #14 
"Kyle"
Feb 2005
Somewhere near M52..
38C_{16} Posts 
Okay, what are the cons of skipping stage 2 to go directly to the LL test?

20050311, 16:30  #15  
P90 years forever!
Aug 2002
Yeehaw, FL
3^{2}·19·43 Posts 
Quote:
Of course, the chances are only about 2%, so more likely skipping stage 2 will save you half a day. In short, don't worry about it. 

20050311, 22:48  #16 
"Kyle"
Feb 2005
Somewhere near M52..
2^{2}×227 Posts 
Ahh, so the LL test is where it usually finds the factors then? I was getting my hopes up .

20050311, 23:03  #17  
P90 years forever!
Aug 2002
Yeehaw, FL
3^{2}·19·43 Posts 
Quote:
See http://mersenne.org/math.htm. It might help 

20050311, 23:06  #18  
"Sander"
Oct 2002
52.345322,5.52471
29×41 Posts 
Quote:
Before performing a LL test, we try to find small factors using two different kind of calculations. First, trail factoring is performed. The program just tries all possible factors below a certain value (around 2^67 or so). If a factor is found, the number is composite and can be discarded. A factor can be found any time. After a few minutes, a few hours or not at all. If a factor exists, it will always be found. If trail factoring doesn't succeed, a different method is used. This is called P1 and is what you were doing. P1 will find a factor if the factor1 is 'smooth', that is, it has only small factors. P1 consists of 2 stages, and a factor can be found after each stage (not before!). This method doesn't 'try' all possible numbers, but if a factor is found depends on the properties of the factor itself. This method can however find much larger factors. For more information read the math page on www.mersenne.org If no factor is found, only then will a LL test be done. This test also needs to be completed fully to determine the result. Some things might be a bit simplistic, but i hope this makes things a bit more clear to you. 

20050311, 23:55  #19 
"Kyle"
Feb 2005
Somewhere near M52..
908_{10} Posts 
Yeah, that helps. Thanks . I'm really crossing my fingers that the exponent is prime...

20050522, 01:21  #20 
"Jason Goatcher"
Mar 2005
5×701 Posts 
2 processor/dualcore limited memory question
I don't actually have this problem, but I thought I'd bring it up. A possibility that may become a concern in the future.
I read elsewhere on this site that the second part of p1 testing uses more memory than usual and that got me to thinking. What if, for example, you have a huge farm and limit your RAM based on the usual needs instead of the maximum needs? If you have enough RAM for the second part of P1 testing and the rest is for the other processor when it isn't doing the second part of p1 testing on it's own exponent, what happens if the second processor wants to do P1 testing and detects that it doesn't have enough RAM? Would it abandon that portion, continue on, and potentially waste days worth of time because it wasn't told to wait? I hope I make sense, if I had a scanner I'd draw a picture to explain. 
20050522, 05:05  #21 
Jul 2004
Nowhere
809_{10} Posts 
If not enough memory is avaible for stage 2 of p1 testing it will skip and go straight to ll testing.

20050522, 09:10  #22 
Sep 2002
2·331 Posts 
What moo said is correct.
A slightly different answer is how much memory is needed so P1 stage 2 factoring will be done and not skipped maybe saving having to do a LL and DC or more. From the Prime95.chm file for 24.x (Index > Menus > Choosing CPU > Setting up Available Memory) is the following information. Exponent Minimum Reasonable Desirable 6,000,000 12MB 23MB 33MB 10,000,000 19MB 36MB 53MB 33,000,000 65MB 125MB 185MB But the default is 8MB so P1 stage 2 would be skipped but it prevents the issue of thrashing (virtual memory being used constantly, ie the hard drive being used for virtual memory which is very slow and would severely impact the reponsiveness of the system and the performance of other programs). George also gave a formula for how much memory he allocates both for day and night given a dual processor and an amount of RAM. For a dual processor it must be less than half of total RAM. (Total RAM  what OS needs) / 2 for night and less for day, about / 4 instead. If your PC has very little RAM ie less than 96 MB it might be best to use 8MB and skip P1 factoring and prevent the thrashing issue. Remember the only part of Mersenne prime testing that uses the large amounts of RAM is during P1 stage 2 factoring, about 12 hours per month. Trial factoring, P1 stage 1, LL/DC (Lucas Lehmer/double check LL) all should work with the default amount 8MB or the minimum from the table 12MB. With 512 or more, even the desirable becomes possible. 
Thread Tools  
Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Coordination thread for redoing P1 factoring  ixfd64  Lone Mersenne Hunters  80  20210119 17:17 
NOT the official forum factoring project thread  jyb  Factoring  2  20130903 16:11 
Yet another basicfactoringquestions thread  davar55  Factoring  24  20110123 23:57 
Perpetual ECM factoring challenge thread...  Xyzzy  Factoring  65  20050905 08:16 
Deutscher Thread (german thread)  TauCeti  NFSNET Discussion  0  20031211 22:12 