20210710, 06:30  #45  
Jun 2003
5125_{10} Posts 
Quote:
Of course, not all SNFS 175 are equal. And the 1.3 might not be the proper value. So, it is a good starting point to check if one or the other is clearly superior, but not definitive. Last fiddled with by axn on 20210710 at 06:30 

20210710, 13:13  #46 
Apr 2010
Over the rainbow
2^{2}×3^{2}×73 Posts 
I think I saw somewhere that
snfs difficulty =(digit lenght30)*1.5 Wich is close to what axn said. 
20210710, 13:34  #47  
Apr 2020
7×67 Posts 
You can use MurphyE scores as given by cownoise/msieve to compare polynomials as long as they have the same degree. Helpfully this is a degree 5 SNFS polynomial, so we can compare it to GNFS polynomials in the right range. The score of ~9e11 is comparable to the score of a typical GNFS130 polynomial. 175/130 = 1.35 so that's a good ratio to use for these numbers.
Quote:
I believe the ratio gets larger as numbers get bigger. 1.42 would suggest SNFS250 is as hard as GNFS176, which it isn't. This must have a typo? (13030)*1.5 = 150... Last fiddled with by charybdis on 20210710 at 13:37 

20210710, 13:53  #48 
"Rich"
Aug 2002
Benicia, California
556_{16} Posts 
Batalov told me this:
The short rule of thumb is gnfs_size < 0.56 * S +30 where S is SNFS difficulty. 
20210711, 09:27  #49 
Aug 2020
5*10398e4;3*2539e3
3×131 Posts 
So the difficulty to factor a cofactor of a "special number" is entirely determined by the size of the special number? Or does the cofactor size also play a role? I guess the latter?
And at roughly which digit length should I switch to c130 parameters? VBcurtis mentioned approximately every 30 bits I should switch +5 digits for the params, but at what starting points? 
20210711, 11:08  #50 
Jun 2003
12005_{8} Posts 
The former. Using the cofactor helps in the final sqrt phase when it is doing the gcd to extract factors. That'll avoid reporting small (previously known, redundant) factors.

20210711, 19:02  #51  
"Curtis"
Feb 2005
Riverside, CA
1001101010111_{2} Posts 
Quote:
That said, the formula given the post before yours allows you to plug in 130 for GNFS and solve for S; I get 180 or so. By the time you're at 200 digits, you ought to test params yourself or study the 14e queue submissions in NFS@home subforum to see what params were chosen for SNFS jobs of similar size. That research should keep you out of trouble of the "oops this job took twice as long as it should have" sense. When in doubt, use the bigger largeprime option. 

20210713, 18:00  #52 
Aug 2020
5*10398e4;3*2539e3
110001001_{2} Posts 
Ok, so I roughly chose the params for a GNFS composite of the same difficulty? 180 would agree with my current plan, I used params.c120 for 520, switched to 125 at 550 and next at 580 would be up.
So far the longest SNFS took about 5 h for sieving, so I'm still far from days. 
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