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Old 2009-01-31, 19:50   #1
(loop (#_fork))
fivemack's Avatar
Feb 2006
Cambridge, England

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Default 32/33 and 15e/16e crossover point

These are with N=2^941-1, rlim=alim=200M, sieving 200M .. 200M+10^4

side lp siever yield time/rel
alg 32 15  6237 2.29344
alg 33 15 11693 1.21814
alg 32 16 13320 2.79733
alg 33 16 25553 1.45897
rat 32 15  8559 1.99026
rat 33 15 16440 1.03673
rat 32 16 17536 2.57357
rat 33 16 33922 1.30827
which looks as if 32-bit large primes and 16e is the right way to go for numbers of this size (changing the siever doubles the yield at a fairly small cost in runtime; lp=33 doubles the yield and the number required at the same time so is no net benefit). Probably rational side 0-300M. rlim=alim=200M was a guess, I'll do some more runs to optimise that.

This would be a Big Calculation with capital Big; 2.6 seconds per relation and we need half a billion, so 40 CPU-years. 16e is a prodigious user of memory (about 4G virtual of which just over 1G used), so this may be more a project for people with clusters than for random home user - indeed, that might be a bit more of a strain on clusters than their administrators really want.
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