20130723, 02:18  #45  
Jun 2012
2^{4}·181 Posts 
Quote:
All looks good but for one thing  for lpba/r of 30, I need ~93M rels which equates to ~60M spec_q. If I am to run spec_q from alim/3 to alim, I need alim of about 90M. Or am I missing something? Can I safely run spec_q to values far greater than alim? For laughs I did run some trials using the 16e siever  great yields but terribly slow. I take it GNFS of 169 is too small for this siever. What's the minimum, 180? 

20130723, 07:10  #46  
Sep 2010
Scandinavia
3·5·41 Posts 
Quote:
I don't know what the best way to compare timings is. I would certainly scale them to account for the fact that larger lpb needs more rels. Quote:
I did not think the yield would be that low. My experiments indicated that the yield would be sufficient. I think you need to raise lpba (and also lim) to get a better yield. I have just assumed that I can not sieve above lim. That could be wrong. From what I've seen the cutoff for the 16esiever is about 180. If I were you I'd raise lpba and try to figure out which region sieves best. I hope I didn't waste too much of your time. At least now we know for sure 67M is too low. 

20130723, 07:23  #47 
"Curtis"
Feb 2005
Riverside, CA
2·2,243 Posts 
It is my (beginner) understanding that we can sieve above alim, but yield drops off; if we go too far, we find precious few unduplicated relations. If you look at Rich's parameters in the 4708 thread in aliquot forum (link: http://mersenneforum.org/showpost.ph...postcount=2124), you'll see he has alim at 20M, but plans to sieve from 10M to 34M. I'm not sure why he isn't sieving 710M, but his plan indicates it's no big deal to sieve even 40% above alim.
Curtis Last fiddled with by VBCurtis on 20130723 at 07:24 Reason: added link 
20130723, 08:33  #48 
(loop (#_fork))
Feb 2006
Cambridge, England
6,323 Posts 
I find that changing alim doesn't change yieldperrelation very much. Sieving above alim is really not an issue, but once you're at 2.5x or 3x alim the yield does start to drop off.
Duplication rate is mostly a function of the siever used, but it's obviously a bit difficult to measure in small samples. I used 16e for a 197digit gnfs and for a 947bit snfs, I think that's about the middle of its useful range. For C180 or the 249digit SNFS I'm doing on and off, I'd be on 15e 
20130723, 08:47  #49 
Just call me Henry
"David"
Sep 2007
Cambridge (GMT/BST)
3^{4}×71 Posts 
In the 64bit win sievers to remove the 33bit limit change the 1 to a 0 in the following code snippet:
Code:
#if 1 if(max_primebits[i]> 33) { complain("Only large primes up to 33 bits are allowed.\n"); } #endif 
20130723, 09:00  #50 
(loop (#_fork))
Feb 2006
Cambridge, England
6,323 Posts 
That seems rather a lot of relations to aim for, though I suppose it's a C169; for C150scale numbers, I aim for 80M raw relations and that's usually enough.
I would always aim on the large side for lpba/r; you don't need twice as many relations for one more bit of large primes (I'd expect 150M usually to suffice at 31bits, and 250M for 32bits), particularly with the new faster LA step making big matrices less scary. For a C169 I would definitely use 31bit lpba/r. 
20130723, 09:07  #51  
Sep 2010
Scandinavia
3·5·41 Posts 
Quote:
Quote:
How should we be choosing alim then? Or better yet; what is alim? And what are the effects from changing it? 

20130723, 12:16  #52  
Jun 2012
2^{4}×181 Posts 
Quote:
The parameters for composite of GNFS difficulty d are given by r/alim = INT(3*10^(d/37+3)) lpbr/a = INT(d/18+21) mfbr/a = INT(d/5+28) r/alambda = INT(d/26+21)/10 Pure black box approach to be sure, but a sanity check if nothing else. Similar formulas are given for SNFS. 

20130723, 17:24  #53 
Apr 2010
Over the rainbow
2475_{10} Posts 
just a piece of advice : a line like
Code:
msieve151_gpu v np1 "stage1_norm=3e24 stage2_norm=7e23 800000,1000000" nps t 3 Last fiddled with by firejuggler on 20130723 at 17:24 
20130723, 19:04  #54  
"Curtis"
Feb 2005
Riverside, CA
1186_{16} Posts 
Quote:
That said, restricting stage 2 norm in the nps step seems quite useful my baseline is to divide the default msieve norm by 1820. I aim for 200400 hits per day to do npr on, but tighter nps stage2norm may be called for. 

20130723, 19:14  #55 
Apr 2010
Over the rainbow
3^{2}·5^{2}·11 Posts 
what I meant is " don't forget to put a arsh stage2_norm if you use np1 and nps at the same time"
for the composite I work on (the last in the poly thread), it seems that any poly of value has a stage2_norm below 1e+023. If it is higher, it won't produce a *good* poly. 
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