Re: [Libmesh-users] Quick questions about SCALAR variables

[David K. <dav...@ak...>]

On Tue, Mar 20, 2018 at 1:24 PM, Salazar De Troya, Miguel <
sal...@ll...> wrote:

> Seeing the systems_of_equations_ex5 example:
>
>   *   Why is a SCALAR variable of order FIRST and not CONSTANT? I
> understand it is a variable that takes the same value over the whole domain.
>

The order of a SCALAR corresponds to how many extra dofs we add to the
system, so FIRST --> 1 extra dof, SECOND --> 2 extra dofs, etc. The extra
dofs are typically used to impose constraints, as you probably know, so
sometimes it's useful to choose a higher order SCALAR if you have more than
one constraint to impose.

We could have restricted SCALAR to be CONSTANT, as you suggested, but then
you'd have to add extra SCALAR variables each time you want another
constraint, rather than just increasing the SCALAR order.


>   *   How are SCALAR variables partitioned and to which processor are they
> sent?
>

IIRC we stick them at the end, so typically the last (i.e. (rank-1)^th)
processor will own all the SCALARs.

David