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[Lapack] Lapack Advice


The routine you want to look at is DGEEV. But this is really complicated. I do 
not advise you to do that.

You might want to develop your own 6-by-6 solver based on the QR algorithm 
directly.
(Check any numerical linear algebra book.) For 6-by-6, this is not that hard 
and most of the
recent development have been targeting larger sizes. The plain QR algorithm 
from the 70s
is just fine for 6-by-6. So you reduce your matrix to Hessenberg form, find a 
shift, apply a QR step
on the Hessenberg form, deflate when needed, etc. This is a standard project 
for graduate students
when they take a Numerical Linear Algebra class. It is probably better to go 
that road than to try to
translate the LAPACK code. J.

On Jul 20, 2012, at 1:50 AM, Roly Whear wrote:

Good Morning

I was wondering if you could help with some advice on which lapack routine I 
should use for the following problem (the maths is getting a bit beyond me).

I'm looking to get the rigid body modes of a mass on a set of springs. Sorting 
out the mass and stiffness matricies to get the characteristic equation has 
been relatively straight forward which leaves me with a 6x6 non symmetric 
matrix. All I'm after are the real Eigenvalues and vectors.

The plan is to rework the C or fortran code into VB in Excel if it will work.

Any advice gratefully received

Thanks

Roly Whear
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