[petsc-users] Neumann BC with non-symmetric matrix

[Mark Adams]

On Mon, Feb 29, 2016 at 5:42 PM, Boyce Griffith <griffith at cims.nyu.edu>
wrote:

>
> On Feb 29, 2016, at 5:36 PM, Mark Adams <mfadams at lbl.gov> wrote:
>
>
>>> GAMG is use for AMR problems like this a lot in BISICLES.
>>>
>>
>> Thanks for the reference. However, a quick look at their paper suggests
>> they are using a finite volume discretization which should be symmetric and
>> avoid all the shenanigans I'm going through!
>>
>
> No, they are not symmetric.  FV is even worse than vertex centered
> methods.  The BCs and the C-F interfaces add non-symmetry.
>
>
> If you use a different discretization, it is possible to make the c-f
> interface discretization symmetric --- but symmetry appears to come at a
> cost of the reduction in the formal order of accuracy in the flux along the
> c-f interface. I can probably dig up some code that would make it easy to
> compare.
>

I don't know.  Chombo/Boxlib have a stencil for C-F and do F-C with
refluxing, which I do not linearize.  PETSc sums fluxes at faces directly,
perhaps this IS symmetric? Toby might know.


>
> -- Boyce
>
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