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[Octave-bug-tracker] [bug #37336] Incorrect result of rcond with Netlib
From: |
Sébastien Villemot |
Subject: |
[Octave-bug-tracker] [bug #37336] Incorrect result of rcond with Netlib LAPACK |
Date: |
Wed, 12 Sep 2012 16:19:11 +0000 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:10.0.7) Gecko/20100101 Firefox/10.0.7 Iceweasel/10.0.7 |
URL:
<http://savannah.gnu.org/bugs/?37336>
Summary: Incorrect result of rcond with Netlib LAPACK
Project: GNU Octave
Submitted by: svillemot
Submitted on: mer. 12 sept. 2012 16:19:10 GMT
Category: Libraries
Severity: 3 - Normal
Priority: 5 - Normal
Item Group: Incorrect Result
Status: None
Assigned to: None
Originator Name:
Originator Email:
Open/Closed: Open
Discussion Lock: Any
Release: 3.6.2
Operating System: GNU/Linux
_______________________________________________________
Details:
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.
_______________________________________________________
File Attachments:
-------------------------------------------------------
Date: mer. 12 sept. 2012 16:19:10 GMT Name: burp.mat Size: 216 o By:
svillemot
<http://savannah.gnu.org/bugs/download.php?file_id=26542>
_______________________________________________________
Reply to this item at:
<http://savannah.gnu.org/bugs/?37336>
_______________________________________________
Message posté via/par Savannah
http://savannah.gnu.org/
- [Octave-bug-tracker] [bug #37336] Incorrect result of rcond with Netlib LAPACK,
Sébastien Villemot <=
- [Octave-bug-tracker] [bug #37336] Incorrect result of rcond with Netlib LAPACK, John W. Eaton, 2012/09/12
- [Octave-bug-tracker] [bug #37336] Incorrect result of rcond with Netlib LAPACK, Sébastien Villemot, 2012/09/13
- [Octave-bug-tracker] [bug #37336] Incorrect result of rcond with Netlib LAPACK, Jordi Gutiérrez Hermoso, 2012/09/13
- [Octave-bug-tracker] [bug #37336] Incorrect result of rcond with Netlib LAPACK, John W. Eaton, 2012/09/13
- [Octave-bug-tracker] [bug #37336] Incorrect result of rcond with Netlib LAPACK, John W. Eaton, 2012/09/13
- [Octave-bug-tracker] [bug #37336] Incorrect result of rcond with Netlib LAPACK, Sébastien Villemot, 2012/09/14
- [Octave-bug-tracker] [bug #37336] Incorrect result of rcond with Netlib LAPACK, John W. Eaton, 2012/09/14