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Old 2020-08-16, 01:14   #117
Apr 2020

2×32×13 Posts

Originally Posted by charybdis View Post
A further trawl through the documentation reveals that a lambda of mfb/lpb + 0.1 is used if we leave it unspecified.
Despite what sieve/README.descent says ("in the first case, lambda defaults to mfb0/lpb0+0.1 as everywhere else in cado-nfs"), it looks like I was wrong, and presumably that readme file is outdated.

From sieve/las-norms.cpp:
    /* when lambda = 0 (automatic), we take mfb/lpb + 0.3, which is
       experimentally close to optimal in terms of seconds per relation
       (+ 0.2 might be even better on the rational side) */
    if (lambda == 0.0)
        lambda = 0.3 + (double) sc.sides[side].mfb /
            (double) sc.sides[side].lpb ;
So the default lambda0 for lpb0=31, mfb0=58 is actually 2.17 not 1.97. Probably worth trying ~2.05 on my next run then.

Last fiddled with by charybdis on 2020-08-16 at 01:21
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