bugGNU Octave - Bugs: bug #30092, eig/eigs: possibly incorrect...

 
 

bug #30092: eig/eigs: possibly incorrect result of eigenvalue matrix

Submitter:  None
Submitted:  Wed 09 Jun 2010 09:11:39 AM UTC
   
 
Category:  None Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Incorrect Result
Status:  Invalid / Not an Octave Bug Assigned to:  None
Originator Name:  massimiliano culpo Originator Email:  -email is unavailable-
Open/Closed:  * Closed Release:  * 3.3.51
Operating System:  * GNU/Linux Fixed Release:  None
Planned Release:  None
* Mandatory Fields

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Wed 09 Jun 2010 04:58:07 PM UTC, comment #2: 

To obtain unitary eigenvectors the matrix needs to be normal (B'*B = B*B'), but your matrix is not.

Muhali <muhali>
Wed 09 Jun 2010 10:02:00 AM UTC, comment #1: 

I am sorry for the noise, I just made a stupid error as B is not symmetric nor hermitian. Please close the thread. Sorry again.

Anonymous
Wed 09 Jun 2010 09:11:39 AM UTC, original submission:  

The following code produces a wrong result:

octave:1> B = [1,2; 0 4]
B =

   1   2
   0   4

octave:2> [V,D] = eig(B)
V =

   1.00000   0.55470
   0.00000   0.83205

D =

Diagonal Matrix

   1   0
   0   4

octave:3> V'*V
ans =

   1.00000   0.55470
   0.55470   1.00000

The matrix V is not unitary at all. I wonder if anyone can reproduce this bug , or if it is a problem of my installation of octave.

This happens with octave 3.2.4 and 3.3.51+ compiled on Ubuntu 9.10. I don't know if the information can be useful, but I linked against qrupdate at compile time.

The same happens with eigs. Try for instance with the matrix:

octave:5> C = kron(eye(3,3),B)
C =

   1   2   0   0   0   0
   0   4   0   0   0   0
   0   0   1   2   0   0
   0   0   0   4   0   0
   0   0   0   0   1   2
   0   0   0   0   0   4

M.

Anonymous

 

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  • -email is unavailable- added by rik5 (Updated the item)
  • -email is unavailable- added by muhali (Posted a comment)
  • -email is unavailable- added by None (Submitted the item)
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    Follow 2 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2010-06-09 rik5 StatusNone Invalid / Not an Octave Bug
        Open/ClosedOpen Closed

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