[petsc-dev] ML Reuse redux

[Jed Brown]

On Fri, Aug 26, 2011 at 13:19, John Fettig <john.fettig at gmail.com> wrote:

> When you are solving a
> series of equations, where the nonzero pattern stays the same but the
> values change, shouldn't it make sense to offer an option for AMG
> solvers which changes the matrices used on the levels but does not
> recompute the restriction/interpolating matrices?
>

Smoothed aggregation is not a purely symbolic operation, it actually uses
the matrix entries to compute the interpolation operator. Now if the matrix
entries are not changing too quickly, the old interpolants might still be
good, in which case it would be nice to only update the Galerkin coarse
level operators.

With ML, there is a technical problem that we don't get the interpolation
back in a PETSc Mat, so we can't use PETSc MatPtAP(). I don't know if they
have a similar function that is callable by users, or another way to only
update the Galerkin operators without redoing the smoothed aggregation.
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