unsymmetric eigenvalue problem

Patrick.Alken@colorado.edu Patrick.Alken@colorado.edu
Thu May 18 16:43:00 GMT 2006

On Thu, May 18, 2006 at 11:21:33AM -0500, Linas Vepstas wrote:
> On Wed, May 17, 2006 at 02:45:10PM -0600, Patrick.Alken@colorado.edu wrote:
> >
> >   I have recently needed to compute eigenvalues of unsymmetric
> > matrices,
> When I hit ths problem, someone recommended LAPACK, which
> I then used happily (routine DGEEV). This mailing list has
> seen occasional discusions about how to wrap/merge/whatever
> LAPACK routines with gsl (a technical problem is that LAPACK
> uses the fortran calling convention, making it ugly in C.)

LAPACK I believe uses the same QR algorithm which I have been
implementing, so if I can make it as robust as LAPACK's
implementation it should be a far better alternative than
linking to fortran code.

> > +              f *= FLOAT_RADIX;
> Is this right? isn't there a  "DOUBLE_RADIX" ?

I don't believe there is any standard define for the radix of
the floating point unit. The 'float' and 'double' radixes are
always the same of course - it is the base which the FPU uses
to represent float/double numbers. I used "FLOAT" to refer
to the floating point unit rather than float vs double.

As a side note, I noticed there is an underflow issue in the
patch I submitted yesterday which shows up for larger matrices
8x8+. I will try to fix this asap.

Patrick Alken

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