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Incorrect result of rcond with Netlib LAPACK
From: |
Sébastien Villemot |
Subject: |
Incorrect result of rcond with Netlib LAPACK |
Date: |
Wed, 12 Sep 2012 18:03:29 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.4 (gnu/linux) |
Hi,
I attach a MAT-file containing a 2x2 matrix (Finf), whose rcond is
different depending on the flavor of LAPACK that I use.
With Netlib LAPACK:
octave:2> rcond(Finf)
ans = 0.40463
With Atlas' LAPACK:
octave:2> rcond(Finf)
ans = 0
MATLAB gives 5.5511e-17.
Since the matrix is quasi-singular, the right answer is (almost) zero. A
value of 0.4 is plain wrong.
I cannot determine if this is a bug in Netlib LAPACK or Octave. I wrote
a C program reading the matrix with libmatio then calling dgetrf+dgecon
and I get the right result with both versions of LAPACK, so this points
towards a bug in Octave, but I am still unsure.
I am quite puzzled by this issue, so I would be happy to hear your
feedback.
Thanks,
burp.mat
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- Incorrect result of rcond with Netlib LAPACK,
Sébastien Villemot <=