[petsc-users] Problem with -pc_type gamg

[Jed Brown]

On Fri, Sep 14, 2012 at 5:11 PM, Randall Mackie <rlmackie862 at gmail.com>wrote:

> If you would be interested, I could dump the matrix and send it to you to
> see if you can figure out a fix.
> I have no idea if GAMG would even be a good preconditioner (this is a
> ill-conditioned EM
>

This is very important information. What specific EM system are you
solving? Is the shift, positive, negative or complex? What discretization.
What scale do you need to solve and how performance-sensitive is the
application.

These problems can be huge rabbit holes for multilevel methods, depending
on the parameter range and necessary scale. Efficient solvers will require
extra work since black-box methods cannot cheaply determine things like the
large curl-curl null space.

PETSc folks: We should make an example using auxiliary space
preconditioning so that we can have an FAQ on this.


> problem), but
> I have reasons to believe that MG in general, if done right, would work. I
> was hoping to test this
> with the GAMG preconditioner, without having to do too much work on
> interpolation operators, etc.
>
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