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Old 2006-03-14, 13:09   #4
xilman
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May 2003
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Quote:
Originally Posted by R.D. Silverman
Hi,

Has anyone else ever encountered an error from the CWI solver
that says "too many orthogonal vectors" near the very end of the
computation?

I just got this message while doing the LA for 2,815-.

It is possible that I have some kind of memory/hardware problem.
This is the second time I have seen this. The last time I re-filtered
the data, re-ran the solver and things were fine.

Last night I tried backing up the computation to the last saved
checkfiles, but still had the same problem at the end.

I did some memory diagnostics with the BIOS, but turned up nothing.

Tonight, I will modify the software to ignore the condition and continue
the computation anywhere, but I do not expect success. I will burn
a CD, transfer the data to another machine and try re-running with the
same matrix, rather than re-filtering. This will tell me if it is likely a
software bug or a hardware problem.

But I will have to wait another 8 days for the result.

Ideas, anyone?
I've seen it, and discussed it with Peter Montgomery. We never came to any firm conclusions, other than that the matrix should not be too over-square (very unlikely in your case, given your experience, though I mention it for the possible edification of other readers) and that sometimes there are too many duplicated rows in the matrix. Peter modified the code to look for the latter. A few are normal --- usually corresponding to factorbase primes which are factors of the full SNFS number.

The only practical solution we ever found was to refilter and produce a slightly different matrix. I will be slightly surprised if subsequent runs produce a different and more useful answer. If it does, it may be an indication that the initial random vectors chosen at the start of the algorithm turned out not to be useful. I don't remember whether I've ever seen that happen in practice.


Paul

Last fiddled with by xilman on 2006-03-14 at 13:09
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