[Octave-bug-tracker] [bug #42646] Error in implementation of logm

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?42646>

                 Summary: Error in implementation of logm
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Sun 29 Jun 2014 07:05:51 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
             Assigned to: None
         Originator Name: uhlmannj
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.8.1
        Operating System: Any

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Details:

The logm function fails for many types of matrix, e.g., any triangular matrix
of ones. 

> M = tril(ones(2));
ans = 

   1 0
   1 1

> logm(M)
warning: inverse: matrix singular to machine precision
ans =

   0 0
   0 0

M is nonsingular unit eigenvalues and thus has a logarithm, e.g.:

> expm([0 0; 1 0]) 
ans =

   1 0
   1 1






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