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

 
 

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

Submitted by:  None
Submitted on:  Wed 09 Jun 2010 09:11:39 AM UTC  
 
Category: NoneSeverity: 3 - Normal
Priority: 5 - NormalItem Group: Incorrect Result
Status: InvalidAssigned to: None
Originator Name: massimiliano culpoOriginator Email: -unavailable-
Open/Closed: ClosedRelease: 3.3.51
Operating System: GNU/Linux

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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 = BB'), 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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  • -unavailable- added by rik5 (Updated the item)
  • -unavailable- added by muhali (Posted a comment)
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    Date Changed By Updated Field Previous Value => Replaced By
    Wed 09 Jun 2010 09:16:15 PM UTCrik5StatusNone=>Invalid
      Open/ClosedOpen=>Closed

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