Søren Hauberg wrote:

> tor, 22 01 2009 kl. 14:19 +0100, skrev Jaroslav Hajek:

>

>> On Thu, Jan 22, 2009 at 1:39 PM, Søren Hauberg <

[hidden email]> wrote:

>>

>>> tor, 22 01 2009 kl. 13:35 +0100, skrev Francesco Potortì:

>>>

>>>>> Is it possible to force 'eigs' to produce real eigenvalues? I'm

>>>>> computing eigenvalues of a real symmetric matrix, but I'm still getting

>>>>> complex eigenvalues (numerical issues I guess), so it would be nice if I

>>>>> could force them into being real.

>>>>>

>>>> Have you looked at the numbers? If the imaginary part is very small

>>>> compared to the real one, you can just discard it using real(). If not,

>>>> you may have stability problems.

>>>>

>>> Yeah, I can just discard them using real (they are indeed quite small).

>>> It just seems to me that it would be better if I could constraint 'eigs'

>>> to working only with real values.

>>>

>>>

>> I think this is a bug - eigs should discover a symmetric case.

>>

>

> If I understand the documentation correctly it should even be possible

> to force the problem to be treated as symmetric by passing

>

> struct ("issym", true)

>

> as an option. This, however, still produced complex results.

>

> Søren

>

Is the matrix real or complex.. If the matrix is complex, as the code

stands the symmetry is ignored..

D.

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David Bateman

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