Putting a peculiar multilevel scheme into DMMG?

Matthew Knepley knepley at gmail.com
Sun Dec 13 10:11:07 CST 2009

Not sure if you would need API additions. Can't everything you describe be
handled through defining the grid, operator, residual, and projections?


On Sun, Dec 13, 2009 at 8:59 AM, Jed Brown <jed at 59a2.org> wrote:

> I can think of a few ways to implement the following multilevel scheme,
> but I'm not sure if it's possible/desirable to have DMMG to manage it.
> Finest level       (A)  : DMComposite[DA_2D(dof=1),DA_3D(dof=4+)]
> Intermediate level (B)  : DM_2D(dof=3)
> Coarsest levels    (C1) : DM_2D(dof=1)
>  OR               (C2) : DM_2D(dof=3)
> No matrices are assembled on level A, but the smoother involves 1D
> solves within columns.  Restriction A->B involves integration and
> discarding "slow" quantities.  Assembly is available for Level B and
> higher matrices.  There are two coarsening strategies after B, one
> involves a fieldsplit where the coarsest grids are only for a scalar
> problem, other coarsens B directly.
> I think grid sequencing and nonlinear multigrid are not important here
> because level B does not contain the long time scales for which
> globalization would be challenging.  So this hierarchy is strictly for
> preconditioning.  The DMMG interface is rather different from other
> components and I recall Barry saying he would like to eventually get rid
> of it.  Is there an advantage to using it here?  Unless I'm missing
> something, it would require some additions to the API (which I can do if
> it is the right thing to do).
> Jed

What most experimenters take for granted before they begin their experiments
is infinitely more interesting than any results to which their experiments
-- Norbert Wiener
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