[Octave-bug-tracker] [bug #38577] Eig returns non-unitary transformation matrix

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?38577>

                 Summary: Eig returns non-unitary transformation matrix
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Sa 23 Mär 2013 16:44:18 UTC
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: Peter
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.6.2
        Operating System: GNU/Linux

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Details:

Dear All,

the following code


M=200;
A=zeros(M,M);

Index1= ( M - mod(M,2) ) / 2;

A(M,M-Index1) = -1.0;
A(M-Index1,M) = -1.0;

[ U, E ] = eig( A );

z = max ( abs( diag( U * U' ) - ones (M,1)))


produces a '1' as result, instead of  a numerical zero. 
Tested on octave 3.2.4 and 3.6.2.
It looks like one eigen vector is just a zero vector.
On 3.6.2 it work for M<130, and fails for M >=130.
At least I checked until M=1000.

Peter





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