Petsc command to get the conditionning of matrices
Jed Brown
jed at 59A2.org
Thu Jul 16 05:44:36 CDT 2009
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
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