[petsc-users] Eigenvalues calculations in PETSc

Matthew Knepley knepley at gmail.com
Wed Feb 26 16:46:19 CST 2014

On Wed, Feb 26, 2014 at 2:41 PM, Qin Lu <lu_qin_2000 at yahoo.com> wrote:

> Hello,
> I need to find the spectrum of the a large linear system (over 100,000
> unknowns). Option -ksp_compute_eigenvalues_explicitly ran out of memory
> since the matrix is too big, then -ksp_compute_eigenvalues only gave a
> small number of eigenvalues (around 30). My questions are:
> 1. Is the number of computed eigenvalues determined by the number of GMRES
> iterations to converge?
> 2. Can PETSc give the extreme eigenvalues now that the number of computed
> eigenvalues is limited?

It will help to understand why you want these.


> Thanks a lot for your info,
> Qin

What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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