[Octave-bug-tracker] [bug #43875] warning: matrix singular to machine precision for triangular matrices

[Marco Caliari]

URL:
  <http://savannah.gnu.org/bugs/?43875>

                 Summary: warning: matrix singular to machine precision for
triangular matrices
                 Project: GNU Octave
            Submitted by: caliari
            Submitted on: Tue 23 Dec 2014 01:55:50 PM GMT
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.8.1
        Operating System: GNU/Linux

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Details:

Dear all,

if I try to solve the system


A = [1,2,3;4,5,6;7,8,9]; A \ ones(3,1)


I get the warning about the singularity of the matrix (rcond  = 1.54e-18). If
I take the U of its LU factorization [L, U] = lu(A) and the same rhs, I get no
warning, although rcond (U) = 2.59e-18.
Is this desired? Matlab gives the warning in both cases.

Cheers,

Marco




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