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[Lapack] What's the best lapack routine to use?


If your matrix is symmetric banded, then DSBEV, DSBEVX and DSBEVD should
be better than DSYEV, DSYEVX, DSYEVR or DSYEVD. Julien.


On 1/15/15, 3:52 PM, "Kevin Cahill" <kevinecahill@Domain.Removed> wrote:

My matrix is banded and I want all the eigenvalues.
So I guess DSYEV is what I need.
Thanks.

On Jan 15, 2015, at 9:08 AM, Langou, Julien
<Julien.Langou@Domain.Removed> wrote:


Do you want all the eigenvalues or just a  few of them?
Is the matrix dense or is the matrix sparse?

If you have a dense symmetric matrix and want all of its eigenvalue then
you can use LAPACK subroutines: DSYEV, DSYEVD, DSYEVR, or DSYEVX.
Which is the best?
DSYEV is fine enough if you want only the eigenvalues (and not the
eigenvectors). 
DSYEVR or DSYEVD are good for eigenvector computation.
Which one is better kind of depends on the platform and the problem at
hand. Both are good enough.

Cheers, 
Julien.


On 1/14/15, 6:38 PM, "Kevin Cahill" <kevinecahill@Domain.Removed> wrote:

What's the best lapack routine to use to find the eigenvalues of a huge
real symmetric matrix whose eigenvalues are positive or zero?

Best wishes,
Kevin





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