Sieving question

[jasong]

Because I'm obsessive-compulsive, I tend to worry about things that are only important to me. I have a Linux AMD machine that I use for sieving, and a Pentium-D that I use for LLRing. My brain has decided that it is REALLY important that I sieve until the core on my Linux box is sieving less than 5 factors for every one one of my Pentium-D cores LLRs.

Is there a command in sr5sieve that will tell me how many factors are expected in a range without having to mess around with the files to get the answer?

[jasong]

Never mind. Apparently, my self-applied rule means I should only LLR.

[geoff]

Originally Posted by jasong

Is there a command in sr5sieve that will tell me how many factors are expected in a range without having to mess around with the files to get the answer?

The formula sr5sieve uses N*(1-log(P0)/log(P1)), where N is the number of candidates remaining and P0-P1 is the sieve range.

You can start sr5sieve as `sr5sieve -v -p P0 -P P1' to get this estimate, but it is probably easier just to use a calculator.

[Rincewind]

Another sieving question, but I don't want to start a new topic:
I used an older version of sr5sieve (I think it was 1.0) I think I should read the name before downloading the file. Is this a problem, it is possible that I missed some factors?

[masser]

Geoff can probably tell you what versions were slightly faulty - a good check is to see if you got close to the expected number of factors.

Make sure you download the most recent versions of sr(x)sieve! There have been huge improvements since version 1.0...

[Rincewind]

I noticed some improvements, my Pentium 1600 MHz (version 1.x) sieves ~44000 p/sec,
my Pentium 800 MHz (version 1.5.15) sieves ~35000 p/sec.
I expected a bigger difference.

[masser]

Your 800 Mhz machine is probably a P3, while the 1.6 Ghz machine is probably a P4. IIRC, P4's are not as good at sieving as some of the other processors. I would try the latest version on the 1.6 Ghz machine - that would be a better comparison.

[Rincewind]

OK, that's new for me, an you're right, its a P3 and a P4. I thought the 800MHz CPU has this performance only because I used the newer version.
I just started to resieve my range (lost 12 percent) with the new version to find every factor.

[geoff]

Originally Posted by Rincewind

Another sieving question, but I don't want to start a new topic:
I used an older version of sr5sieve (I think it was 1.0) I think I should read the name before downloading the file. Is this a problem, it is possible that I missed some factors?

All x86 versions before 1.4.0 had a fault in the mulmod code that would start to give incorrect results when p became larger than 2^46, or maybe as low as 2^42 in some rare cases. These errors would become more frequent as p increases. At the current sieve ranges (8000G+) these errors could be starting to have an effect.

[geoff]

Originally Posted by geoff

All x86 versions before 1.4.0 had a fault in the mulmod code that would start to give incorrect results when p became larger than 2^46, or maybe as low as 2^42 in some rare cases.

That was not quite correct, sorry:

For versions before 1.4.0 the lowest known p that gave an incorrect result was about 2^46, which is about 70000G. I can't rule out the possibility of some bad results between 2^42 and 2^46, but I don't think the current sieve ranges at about 8000G would be significantly affected. Sorry if you repeated any work unnecessarily.