[petsc-users] Eigenvalues calculations in PETSc

[Jed Brown]

Richard Mills <rtm at utk.edu> writes:

> Qin,
>
> Krylov methods will find the extreme eigenvalues first (unless you do
> something in particular to get at the interior values), so this is what you
> are getting from PETSc.
>
> Another thing to keep in mind is that the eigenvalue estimates using the
> Hessenberg matrix from GMRES can be pretty terrible.  If you want something
> better, you may want to use something like Arnoldi/Lanczos or
> Jacobi-Davidson.  Yousef Saad's book at
> http://www-users.cs.umn.edu/~saad/eig_book_2ndEd.pdf offers some great
> explanations of these methods, which you can use via the PETSc-based SLEPc
> package.

Agreed.  Use SLEPc if you want actual eigenvalues or eigenvectors.  You
can target wherever you want.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 835 bytes
Desc: not available
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20140227/d8b27434/attachment.pgp>