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

[Boyce Griffith]

> 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.

-- Boyce
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