[Octave-bug-tracker] [bug #41065] Single precision matrix inverse gives bogus singular matrix warning

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?41065>

                 Summary: Single precision matrix inverse gives bogus singular
matrix warning
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Thu 02 Jan 2014 02:25:17 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Zsbán Ambrus
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.6.2
        Operating System: Microsoft Windows

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Details:

Dear octave devs,

It appears that the inv function can give a bogus warning about the input
being a singular matrix even when I use a single precision matrix that is very
far from singular.  The resulting inverse matrix I get seems to be correct,
only the warning is wrong.  

Here is a transcript for the bug.


e:\ambrus\f\stereo\tmp\m>octave --no-init-file
GNU Octave, version 3.6.2
Copyright (C) 2012 John W. Eaton and others.
This is free software; see the source code for copying conditions.
There is ABSOLUTELY NO WARRANTY; not even for MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  For details, type `warranty'.

Octave was configured for "i686-pc-mingw32".

Additional information about Octave is available at http://www.octave.org.

Please contribute if you find this software useful.
For more information, visit http://www.octave.org/help-wanted.html

Read http://www.octave.org/bugs.html to learn how to submit bug reports.

For information about changes from previous versions, type `news'.

 - Use `pkg list' to see a list of installed packages.
 - MSYS shell available (C:\Program Files (x86)\Octave-3.6.2\msys).
 - Graphics backend: qt.

octave-3.6.2.exe:1> inv(single(eye(3)+0))
warning: inverse: matrix singular to machine precision, rcond = 0
ans =

   1  -0  -0
   0   1  -0
   0   0   1

octave-3.6.2.exe:2> 







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