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Old 2009-03-19, 01:33   #17
mklasson
 
Feb 2004

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Quote:
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?
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