20091114, 14:06  #1 
Sep 2009
7E9_{16} Posts 
Oversieving
Roughly how much oversieving is needed to: 1) Minimize total time if all the work is done on one system? 2) Minimize time taken in postprocesing? 3) Minimize peak memory use postprocessing? Thanks in advance. Chris K

20091114, 14:13  #2  
Nov 2008
100100010010_{2} Posts 
Quote:
Last fiddled with by 10metreh on 20091114 at 14:14 

20091114, 20:22  #3 
Tribal Bullet
Oct 2004
2^{4}·13·17 Posts 
The answer depends on the problem size, which determines how much time the linear algebra takes out of the total. For problems that fit comfortably onto one machine, you should stop sieving as soon as a matrix can be constructed. Larger problems can benefit from adding maybe 510% more relations past this point. By the time you get to really huge problems, 50% oversieving may be called for; you get diminishing returns from adding more relations, and if the first matrix will be very difficult then you have to reduce its size by a great deal.

20100312, 17:43  #4 
Bamboozled!
"πΊππ·π·π"
May 2003
Down not across
24622_{8} Posts 
Too much oversieving
I know this has been discussed somewhere on the forum but I can't find the discussion despite having skimread hundreds of posts in the msieve subforum.
A small (c175) SNFS factorization is predicted to take 12.6M relations, in line with previous factorizations of similarly sized numbers. It has already reached that and has gone well beyond it; it is currently well over 16M relations. Even so, the msievefact.py script claims that more relations are needed. Running msieve standalone with nc or nc1 hasn't yet done anything useful. Would someone please point me at the posting where this issue is resolved? Paul 
20100312, 17:47  #5 
Jun 2003
13^{2}·29 Posts 

20100312, 19:55  #6  
Oct 2004
Austria
2·17·73 Posts 
Quote:
Edit @ Xilman: With lpbr/a one bigger than Bsquared used, you might need ~18M relations. Last fiddled with by Andi47 on 20100312 at 19:58 

20100313, 19:29  #7  
Bamboozled!
"πΊππ·π·π"
May 2003
Down not across
2·17·313 Posts 
Quote:
I gave up in the end and reran the factorization from scratch on a 64bit RHEL box. The failing system ran 64bit Win7. Everything went fine and the program is now in the sqrt phase, which I confidently expect to fail. When it happens, I'll transfer everything to a Windoze system to get the factors. Luckily, I have both Linux and Windoze machines, both Perl and Python drivers available. Ho hum. Paul P.S. Yup, it failed ... 

20100313, 21:51  #8  
Sep 2009
3^{4}×5^{2} Posts 
Quote:
Chris K 

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