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Old 2009-03-19, 01:33   #17
Feb 2004

2×3×43 Posts

Originally Posted by bsquared View Post
For larger inputs say > 85 digits I'd start with the table in the GMP-ECM readme file and target doing ECM to, say, the 2/9*N digit level if the input is QSable or 1/3*N digit level if the input would otherwise need NFS.
I think 1/3*N might be a bit excessive. For a 120-digit composite that amount of ecm (factors <= 40 digits using gmp-ecm-readme settings) would seem to take me ~10 cpu-hours, whereas just pounding on it with ggnfs takes slightly more than twice that time. That's too much ecm, isn't it?

I did some experimental benchmarking today to find good ecm levels for <65 digits. It's a shame it's not that easy for c100+.

Hm, come to think of it, as nfs has better asymptotics shouldn't the ecm scaling factor for nfs be smaller than the corresponding one for qs? I.e. using 2/9*N for qs and 3/9*N for nfs seems inherently wrong. I realise they're both fuzzy guidelines, but don't you agree?

Maybe something like 11+1/5*N would be better for nfs? Or maybe I'm just wrong. In any case, how much ecm do you people often running big nfs jobs normally do?
mklasson is offline   Reply With Quote