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Old 2013-02-26, 01:32   #1
skan
 
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Apr 2012

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Default NFS on smaller numbers?

How can I force Yafu to use NFS instead of SIQS even on smaller numbers? (without recompiling)
Just to test speed.
next time you upload the windows version, could you please lower that limit?

thanks

Last fiddled with by skan on 2013-02-26 at 01:35
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Old 2013-02-26, 01:35   #2
Dubslow
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"nfs(num)" as opposed to "factor(num)"?

There's a built in limit to Msieve at like 80 digits or something; it's not really possible to do NFS on anything smaller than that.
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Old 2013-02-26, 03:27   #3
bsquared
 
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The built in limit in YAFU is 85 digits. For Win32 the crossover is probably around 100 digits. For sure it is more than 85 digits, so you should be able to run enough tests to see the speed crossover.
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Old 2013-02-26, 07:21   #4
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skan, NFS on numbers shorter than 90 digits is definitely a waste of CPU power

I ran tune yesterday evening with yafu 1.34 on Core i7-2670QM running 64-bit Linux, which estimated the NFS / SIQS crossover at 98 digits - despite usage of 64-bit ggnfs sievers. The crossover is higher than with previous versions of yafu, in line with the announced recent improvements to the SIQS code.
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Old 2013-02-26, 12:02   #5
skan
 
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Hi

I know that on numbers smaller than 90 digits NFS is not the faster but I just would like to try it for number of 60 digits. Just to play with.
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Old 2013-02-26, 12:16   #6
henryzz
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SNFS can be useful around that range. I personally don't like the limit as it limits what experimentation you can do. Low digit s/gnfs can be good for experimentation.
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Old 2013-02-26, 13:57   #7
jasonp
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Msieve's postprocessing will take a minimum of around 1 minute, for SNFS or GNFS. Nowadays in 1 minute YAFU can factor a 90-digit input using multiple threads.

The Msieve cutoff is 85 digits for NFS, but that's only a limitation in the polynomial selection. I suppose if your input has an obvious SNFS polynomial then you can do the sieving and then postprocess like normal. To quote another post:


Right now you can run NFS postprocessing on any size number, but modifying polynomial selection to handle numbers smaller than the current limit requires the ability to select degree 3 polynomials and to find GNFS polynomial selection parameters suitable for numbers smaller than the current limit. Both of those would take some time, and in the meantime you'd find that if it works at all then factoring, say, a 60 digit number will take maybe 30 seconds if you're lucky and it doesn't crash, whereas if it does crash then I'd have additional work to do. You know that QS is a better choice at that size (YAFU would finish a 60-digit job in maybe 1 second), so getting the same answer in a much longer time is not useful, especially compared to what I could be doing on the codebase in its place.

Note that the CADO tools can perform complete factorizations down to 60 digits.

Last fiddled with by jasonp on 2013-02-26 at 14:04
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