[petsc-dev] Lagging the numerical factorization for one of the fields of fieldsplit preconditioner

[Jed Brown]

On Tue, Mar 15, 2011 at 20:47, Barry Smith <bsmith at mcs.anl.gov> wrote:

> Do you form the big-assed matrix
> > | A      dg_dx |
> >  | df_dy  df_dx |
>
>   explicitly as one big matrix?  And each time-step you changes values in
> the dg_dx, df_dy  and df_dx parts with MatSetValues?
>
>
>    One fix may be to make PCSetUp() smarter and know the matrix has not
> changed and hence it doesn't have to be refactored (instead of only relying
> on the flag passed to KSPSetOperators()).
>

If you use MatNest (the logical choice with PCFieldSplit, it's a runtime
option except for preallocation), then we could PetscObjectStateQuery() to
decide when sub-objects need to be rebuilt. Seems like a better
general-purpose solution if you want an easy high-level way to control when
things get rebuilt.
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