>>>>
I got the following set of messages today: [Tue Jul 20 16:15:19 1999]
Iteration: 6128000/7812379, ERROR: ROUND OFF (0.4026489258) > 0.40
Possible hardware failure, consult the readme file.
Continuing from last save file.
[Tue Jul 20 16:35:33 1999]
Disregard last error. Result is reproducible and thus not a hardware problem.
I consulted the readme file, but it wasn't very helpful. What is a "ROUND OFF" error? While it's nice that it's reproducible, will it invalidate the result of this LL test? Does the fact that this exponent (7812379) is so close to the FFT size breakpoint (7820000) make this type of error more likely? Thanks, Dan Swanson
The calculations are done in the fft using an irrational base, then converted
back to integer form by rounding. The amount of rounding is monitored. Well
away from the size breakpoints, the roundoff may only be thousandths, or less.
The FFT size breakpoints are determined by estimates of how high an exponent
can safely (without roundoff error) be run on the shorter faster size.
When roundoff exceeds 0.4, it is possible that a memory error or cpu error
caused it. It's also possible that the roundoff was actually greater than 0.5
and rounding to an incorrect integer has occurred. Exponents near fft size
breakpoints, or any that generate both the roundoff error and the reproducible
message are therefore somewhat more likely to fail a double check, and so are
candidates for earlier double checking.
Nonreproducible roundoff errors mean hardware may be unreliable;
reproducible roundoff errors mean fft size breakpoints (& LLtests) may be
unreliable.
Ken
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