At 07:07 PM 6/22/2008 +0200, you wrote: >Ken Kriesel wrote : > >> For a hypothetical pool of machines of constant reliability, >> the error rate per trillion operations (or should that be per >> hour of 100% cpu utilization?) would be about constant. >> The number of operations goes up slightly faster than the >> square of the exponent, so twice the exponent means more than >> 4 times the error rate per exponent. (More iterations, >> performed in more pieces, of slightly lower precision) > >George Woltman increased the reliability of the software to decrease the >error rate (more checking during the LL tests...) > >> It's also possible to have an error in factoring attempts >> yield a false positive for a factor that fails verification. > >Factors are verified when submitted, according to a post by George >Woltman on the Mersenne forum. What could happen are missed factors due >to hardware errors.
My recollection is I've seen the false positive factor case occur (in instances not using primenet). Of course the other factoring error occurs silently (missing a factor that if computation occurred correctly would have been found). >> If I recall correctly, verification of a Mersenne prime is >> run on different software on a different computer >> architecture to maximize the chance of a software bug or >> computer hardware design error from yielding a false >> positive. During the QA effort, comparisons of interim LL >> test residues were made among differing software run on >> differing computer architectures. > >This is only done when a LL test finds an exponent yielding a prime. >Otherwise double-checks are accepted even if done by the same machine >with the same software version if the different shift gives the same 16 >byte residue. > >Jacob Yes, verification of a Mersenne prime is a very special case double-check, so it is done differently than the double check of a negative result. Ken _______________________________________________ Prime mailing list [email protected] http://hogranch.com/mailman/listinfo/prime
