Re: [Libmesh-users] Inferring SparsityPattern for DG discretization

[Vijay S. M. <vi...@gm...>]

That makes a lot more sense. I can loop over the elements depending on
the flux type I use for my discretization and infer the coupled dofs I
need.

Thanks for the help Ben !

On Fri, Nov 7, 2008 at 11:50 AM, Benjamin Kirk <ben...@na...> wrote:
>> A clarification regarding what you said:
>>
>>> The DofMap will add all face neighbor degrees of freedom to an element's
>>> coupled dofs if
>>>
>>> (1) all the variables in the system are discontinuous, or
>>> (2) the command line option '--implicit_neighbor_dofs' is specified.
>>
>> In my system, all variables use disconitnuous basis. And now I tried
>> to run the code with --implicit_neighbor_dofs in command line. But I
>> still get only the local element dofs and not the neighboring element
>> dofs when I populate dofs with the call "dof_map.dof_indices(...)".
>
> Oh, I see what you want.  In your case the sparsity pattern is built up
> properly using the neighbor degrees of freedom, but DofMap::dof_indices(...)
> will always return only the degrees of freedom an element needs to compute
> the solution in that element...
>
>> Is this what is to be expected or did I try something else than what
>> you suggested ? I just need DofMap to tell me which other dof my
>> current dofs are coupled to. From what I understand, your reply
>> answers that but somehow I do not see the same in my code. Am i
>> missing something ?
>
> So, in your case, when you are computing the face contribution between
> 'elem' and 'neighbor', you need DofMap::dof_indices(elem,...) and
> DofMap::dof_indices(neighbor,...).  This is consistent with the fact that
> you will need two FiniteElement objects, one on the local element and one
> for the neighbor.
>
> The total list of Dofs coupled to a given element will be the union of
>
> DofMap::dof_indices(elem,...)
> DofMap::dof_indices(neighbor_0,...)
> ...
> DofMap::dof_indices(neighbor_N,...)
>
> Does that help?
>
> -Ben
>
>