Petsc command to get the conditionning of matrices

[Jed Brown]

STEPHANE TCHOUANMO wrote:

> Is there a way to get the conditionning of my Jacobian matrices? like a command when running my exectable (-ksp_.. or -snes_.. or -pc_..)

I use

-ksp_monitor_singular_value

  estimate at every Krylov iteration, only works with GMRES and CG

-ksp_compute_eigenvalues

  estimate of a few eigenvalues from the iteration (GMRES and CG)

-ksp_compute_eigenvalues_explicitly

  sometimes useful for very small systems, e.g. to find the size of a
  null space while debugging

-ksp_plot_eigenvalues_explicitly

  again, only for very small problems.


Note that these eigenvalues and singular values are not reliable for
eigen-analysis, they are only intended to help understand why iterative
methods are working a certain way.  If you care about accurate
eigen/singular values, use SLEPc.



I noticed a few weeks ago that -ksp_compute_singularvalues didn't work
as advertised.  A few lines needed to be added to KSPSolve(), as for
-ksp_compute_eigenvalues.  I usually use -ksp_monitor_singular_value
instead, so it hadn't bothered me, but it's now in petsc-dev:

  http://petsc.cs.iit.edu/petsc/petsc-dev/rev/3180aa7f49b4


Jed

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 260 bytes
Desc: OpenPGP digital signature
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20090716/c35e0631/attachment.pgp>