[Octave-bug-tracker] [bug #44849] expm() produces incorrect result

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?44849>

                 Summary: expm() produces incorrect result
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Wed 15 Apr 2015 06:19:32 PM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Peter Roopnarine
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.6.4
        Operating System: GNU/Linux

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Details:

I ran expm(), the matrix exponentiation function on several large (n=47 and
n=111) asymmetric square matrices and received unexpected results (numerically
very large). I then compared the output of a much smaller matrix to that given
by the Eigen C++ exp() function and the results differ. The Eigen results are,
I believe, correct. Here is the Octave code:


B = [0,-0.785398,0;0.785398,0,0;0,0,1];
expm(B)
ans =

   0.70711  -0.70711   0.00000
   0.70711   0.70711   0.00000
   0.00000   0.00000   2.71828

Element (3,3) should be 1.
Here is a link to the Eigen page
http://eigen.tuxfamily.org/dox/unsupported/group__MatrixFunctions__Module.html#matrixbase_exp




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