Re: [Libmesh-users] The use of MONOMIAL/XYZ FE_type

[John P. <jwp...@gm...>]

On Wed, May 16, 2018 at 6:53 AM, <li...@si...> wrote:

> Dear developers,
>
>
>
>
> I tried using the MONOMIAL/XYZ FE_type as in the miscellaneous_ex5 example.
>
>
> After simplification under the choice of some parameters, my problem
> reduces to a Laplace equation with Dirichlet boundary condition.
> If a default FE_type is used (system.add_variable ("p", FIRST);), the
> Laplace problem outputs a right result,
> but if a MONOMIAL/XYZ FE_type is used instead (i.e. system.add_variable
> ("p", FIRST, XYZ)),
> the interior part is wrong, it isn't changed from its initial solution
> value (I set zero for the initial value),
> only the boundary is right due to the impose of Dirichlet condition.
> I have implemented the contribution of each element boundary flux as that
> in the miscellaneous_ex5 example.
> I don't know why it fails in the interior part.
>

I'm not sure why XYZ would not work. It's possible that the solution is
actually OK but the error arises in the
ExodusII::write_discontinuous_exodusII() output?

I don't think we have much testing of the XYZ FEType in libmesh or in apps
which use libmesh, so it's possible that i regressed.




> 2.  Another question is, if I want to couple two variables into one
> system, one with a default FE_type and the other with the MONOMIAL/XYZ
> FE_type, is that possible?
> I tried and found that when inserting the contribution of neighbor values
> into the matrix (as "Ken, Kne" in miscellaneous_ex5),
> PETSc error reports that
> ---------------------------------------------------------------
> Argument out of range!
> New nonzero at (13,33164) caused a malloc!
> MatSetValues_MPIAIJ() line 572 in src/mat/impls/aij/mpi/mpiaij.c
> MatSetValues() line 1106 in src/mat/interface/matrix.c
> add_matrix() line 699 in "unknowndirectory/"petsc_matrix.C
> ---------------------------------------------------------------
>
>
> It seems that different FE_types lead to different matrix preallocations,
> the MONOMIAL/XYZ FE_type allows the insert of Ken, Kne but the default
> FE_type does not.
> Can I use the same matrix preallocation for the two variables to allow
> such inserting?
>

And you are using libmesh master? This is interesting, as we are discussing
a similar error right now over on
https://github.com/libMesh/libmesh/issues/1697 that might be related,
although I suspect yours might have more to do with DG sparsity patterns.

-- 
John