Re: [Lapackpp-devel] Problem With EigenVector Calculation for a 3x3 Matrix

[sun <pyt...@gm...>]

Hi, first we know that both results of Lapackpp and Matlab are correct
although sometime some of eigenvectors become mirrored. So in my point of
view, that is not a problem of Lapackpp.

As you concern, if I understand correctly, you are not happy with the
negative sign of eigenvectors.
I think you can self-control the results: Just get the eigenvector of
minimal eigenvalue and then do a simple judgement, if the eigenvector has a
positive sign, it is OK. Otherwise you just reverse the sign by yourself.

sun

On 2/4/07, Satyajit Sarangi <ssa...@gm...> wrote:
>
> Hi Sun,
>           Thanx for your reply. However, if you check the eigen vectors
> you will find that there is an arbitrary change of sign in 1st and 2nd eigen
> vectors which I have shown. also there is a problem that one matrix is kind
> of a mirror image of the other however, with some more negative signs. I am
> using the eigen vectors to estimate normals for a Point in 3D space. So I
> have to use the eigen vector corresponding to the least eigen value. This
> requires me to take the x,y,z value of the eigen vector. So even if the
> vector is a mirror image then it becomes a problem for me. So please comment
> on this. I had noticed the precision but that is not my problem here.
> Regards
> Satyajit