mersenneforum.org What is Legendre Symbol? slowing down sr2sieve?
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 2009-05-20, 11:25 #1 cipher     Feb 2007 211 Posts 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
 2009-05-20, 11:46 #2 kar_bon     Mar 2006 Germany 32·52·13 Posts 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'
 2009-05-20, 11:58 #3 Thomas11     Feb 2003 22×32×53 Posts 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!
 2009-05-20, 13:35 #4 cipher     Feb 2007 211 Posts 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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