#9760: Possible numerical noise doctest failure in sage/matrix/matrix2.pyx on t2
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Reporter: mpatel | Owner: drkirkby
Type: defect | Status: needs_review
Priority: blocker | Milestone: sage-4.5.3
Component: solaris | Keywords:
Author: John Palmieri | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Comment(by drkirkby):
I was just about to write this below, and when I tried to submit it, you
had beaten me to it. I think you have basically confirmed what I thought.
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John,
I'm not exactly sure what's happening in this Sage code - I don't
understand Sage well enough.
But I'm guessing that the the eigenvalues should be real numbers here -
i.e. have zero imaginary component. Any imaginary component present is due
to rounding errors. Would that be right?
If so, I would have thought testing the absolute value was actually the
more sensible test. If the imaginary part of the eigenvalue was -1000,
then the original test would pass, despite my belief that such a huge
negative value would be incorrect. It seems to me the actual test is
fundamentally flawed.
However, adding the abs() would need testing on lots of platforms, so I'm
not suggesting we make that change.
I think in this case, we should change the test to
{{{imag(e) < 1.1e-15}}}
and perhaps open another ticket to change the test, to add the {{{abs()}}}
at a later date.
Does that seem sensible?
Dave
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/9760#comment:11>
Sage <http://www.sagemath.org>
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