libmesh-users

[Libmesh-users] Quick questions about SCALAR variables

[Salazar De T. M. <sal...@ll...>]

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.
  *   How are SCALAR variables partitioned and to which processor are they sent?
Thanks
Miguel

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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

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

[Roy S. <roy...@ic...>]

On Tue, 20 Mar 2018, David Knezevic wrote:

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

This is correct, but please try to avoid writing codes depending on
it; it's one of the upcoming items on our "Stuff I thought would be
fine because small N but which I need to change because INL Ns are
huge" chopping block list (where in this case N is the number of
SCALAR dofs in a problem).
---
Roy

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

[Salazar De T. M. <sal...@ll...>]

Are the SCALAR variables added to the local vectors for each processor?

Miguel

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On 3/20/18, 11:52 AM, "Roy Stogner" <roy...@ic...> wrote:

    
    On Tue, 20 Mar 2018, David Knezevic wrote:
    
    > IIRC we stick them at the end, so typically the last (i.e. (rank-1)^th)
    > processor will own all the SCALARs.
    
    This is correct, but please try to avoid writing codes depending on
    it; it's one of the upcoming items on our "Stuff I thought would be
    fine because small N but which I need to change because INL Ns are
    huge" chopping block list (where in this case N is the number of
    SCALAR dofs in a problem).
    ---
    Roy
    

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

[Roy S. <roy...@ic...>]

On Fri, 23 Mar 2018, Salazar De Troya, Miguel wrote:

> Are the SCALAR variables added to the local vectors for each processor?

As ghosted dof coefficients?  Yes.

The only exception is that, if you have a processor which doesn't own
any elements on which the SCALAR is defined (either because the
processor doesn't own *anything* at the moment or because you have a
subdomain-restricted variable and the processor doesn't own any
elements in the subdomain(s) it's restricted to), it won't get a copy
of the SCALAR values either.
---
Roy