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Old 2009-05-20, 11:25   #1
cipher
 
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Feb 2007

211 Posts
Default What is Legendre Symbol? slowing down sr2sieve?

Recently i tried to sieve 22 K pairs with 1 < n < 50k small range. I used srsieve to sieve upto 1 BIL (approx 50 min) and the file it created sr_2.abcd
i tried using SR2Sieve but the load time for 194000 remaining N values is approx 50 min.
It does something like "Building Legendre symbol lookup table for ________ each k value" and it is already utilizing 1.3 GB of memory Here are the K values i am working on.

Code:
175977945*2^n-1 
178140105*2^n-1  
199140045*2^n-1  
228461805*2^n-1 
228986175*2^n-1 
240924255*2^n-1 
244133175*2^n-1 
249671565*2^n-1 
272605245*2^n-1 
272936235*2^n-1 
281804985*2^n-1 
384158775*2^n-1 
418791945*2^n-1 
445419975*2^n-1 
555567045*2^n-1 
682980375*2^n-1 
687218805*2^n-1 
719053335*2^n-1 
776668035*2^n-1 
828512685*2^n-1 
857996205*2^n-1 
949473525*2^n-1
Can some one explain to me why it is taking so long to start sr2sieve almost 1 hour and why it is using 1.3 GB memory for just 194,000 n values.

In the past i have sieve almost 100's of riesel K with 2 million + n (with sr2sieve) values and it never took such a long time to load or so much memory.

Is there any way i can turn of "Building Legendre symbol " step.

Thanks cipher
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Old 2009-05-20, 11:46   #2
kar_bon
 
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Mar 2006
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turn off the calculation for Legendre symbol tables by option '-x'

or create a cache-file to compute this tables only once: '-C chache.dat'
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Old 2009-05-20, 11:58   #3
Thomas11
 
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Feb 2003

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As Karsten already suggested:
Just turn off the computation of the Legendre symbols by using the "-x" switch.
However, if you're planning larger n-ranges (e.g. up to 500k or 1M), then it might be useful to store the Legendre symbols in a cache file, as sr2sieve runs slightly faster with them...

Good luck!
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Old 2009-05-20, 13:35   #4
cipher
 
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Feb 2007

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if i turn it off using -x switch it runs 20% slower. I guess smart thing to do is to save it, using -c cache.dat

thanks
cipher
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