20100601, 17:58  #23  
Oct 2004
Austria
4662_{8} Posts 
Quote:
Lambdas 2.6 Code:
C:\F_Fun\Wissenschaft\Mathe\GGNFS\BIN>gnfslasieve4I15e r 2801_79.poly o 2801_79_test2.out f 19900000 c 1000 Warning: lowering FB_bound to 19899999. total yield: 2106, q=19901029 (0.34393 sec/rel) Code:
C:\F_Fun\Wissenschaft\Mathe\GGNFS\BIN>gnfslasieve4I15e r 2801_79b.poly o 2801_79_test3.out f 19900000 c 1000 Warning: lowering FB_bound to 19899999. total yield: 2128, q=19901029 (0.36133 sec/rel) 

20100601, 19:09  #24 
May 2008
2107_{8} Posts 
This is strange. The ggnfs siever appears to use a cutoff of fblim^lambda, if I understood the code correctly, but the cado nfs siever (as it exists in the most recent svn) indeed does use 2^(lpb * lambda).

20100601, 19:14  #25 
"Serge"
Mar 2008
Phi(4,2^7658614+1)/2
19·23^{2} Posts 
A couple of weeks ago, I checked the lambda efficiency for a large project: starting from 4.0 down until relations start getting lost significantly and sec/rel gets worse rather than better. Unsurprisingly, I found that the optimum is indeed somewhere at 2.5 and 2.6, so these settings are both good.
(The bottom is flat and to make any conclusions a lot of sieving is needed, but I got a notsowell founded suspicion that 16e may run slightly better with 2.5, while 15e with 2.6. But the difference is tiny, so both values are just fine  and better than 2.4 or 2.7, 2.8. Caveat: this most probably depends on a CPU family. YMMV.) 
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