On Tue, Sep 21, 2010 at 11:28 AM, Andrew Dessler <adessler@tamu.edu> wrote:

Sudheer Phani <bpsu <at> james.hut.fi> writes:

...

Hello All,

I have been encountering some strange problems with the calculation of eigen vectors using python. The problem is with the sign of the eigen vectors calculated. On Very few occasions the eigen vectors calculated using python have an opposite sign than the actual eigenvectors, though the magnitude is correct.

Can any one of you plz help me in this regard and suggest me some

solution

...

if you have encoutered similar problems .

Any help in this regd is appreciated

Thanks in Advace

regds Sudheer

I had a similar experience. However, I solved it when I realized that the eig routine in scipy.linalg does not necessarily return the biggest eigenvalue/eigenvector first. It often does, but not always. Once I realized I had to find the biggest one on my own, the problem was solved.

Note that eigen vectors don't *have* a sign and this is the case even if they are normalized. It is always possible to multiply them by +/- 1, or even by a complex number of magnitude 1 if you are working with complex arrays. Chuck