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Old 2016-07-17, 14:36   #1
ET_
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"Luigi"
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Default ecm with Fermat numbers

Question: with regard to both mprime and gmp-ecm, is it faster running the Fermat number "as-is", or divided by its known factors?

IIRC, mprime was faster using the standard notation and providing the known factors either on the worktodo.txt line or on the lowp.txt file, while gmp-ecn was faster as the number to test grew smaller.

Is it still correct?

Luigi

Last fiddled with by ET_ on 2016-07-17 at 14:37
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Old 2016-08-02, 19:40   #2
GP2
 
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As an experiment, I decided to run mprime twice on the same machine, once with the known factors and once without.

This was using the latest version, 28.9


In other words:

Code:
ECM2=1,2,4096,1,800000000,80000000000,1,"114689,26017793,63766529,190274191361,1256132134125569,568630647535356955169033410940867804839360742060818433"
versus

Code:
ECM2=1,2,4096,1,800000000,80000000000,1
Stage 1:
The two versions ran absolutely identically. The second version was maybe 0.1% faster.

Stage 2:
The first version completed stage 2 in 42% of the time that stage 1 took.

The second version "discovered" a composite factor after stage 1 and stopped without doing stage 2.






PS, when I run ECM exponents I always add:

Code:
ScaleOutputFrequency=1
to prime.txt for convenience, to avoid excessively rapid output for small exponents. See undoc.txt for explanations.

You can also add

Code:
ContinueECM=1
if you like.

Last fiddled with by GP2 on 2016-08-02 at 19:46
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