[petsc-users] Nested field split

[Matthew Knepley]

On Wed, May 17, 2023 at 2:59 PM Barry Smith <bsmith at petsc.dev> wrote:

>
>   Absolutely, that is fundamental to the design.
>
>   In the simple case where all the degrees of freedom exist at the same
> grid points, hence storage is like  u,v,t,p   in the vector the nesting is
> trivial. You indicate the fields without using IS (don't even need to
> change any code)
>
> -pc_fieldsplit_0_fields 0,1,2
> -fieldsplit_pc_fieldsplit_0_fields  0,1
>
> Listing the two complimentary fields
> pc_fieldsplit_1_fields 3
> -fieldsplit_pc_fieldsplit_1_fields  2
> should be optional (I can't remember if it is smart enough to allow not
> listing them)
>
> If you have a staggered grid then indicating the fields is trickery (since
> you don't have the simple u,v,t,p layout of the degrees of freedom)
>

Here we do something similar.

  Thanks,

     Matt


> > On May 17, 2023, at 12:47 PM, Alexander Lindsay <
> alexlindsay239 at gmail.com> wrote:
> >
> > I've seen threads in the archives about nested field split but I'm not
> sure they match what I'm asking about.
> >
> > I'm doing a Schur field split for a porous version of incompressible
> Navier-Stokes. In addition to pressure and velocity fields, we have fluid
> and solid temperature fields. I plan to put all primal variables in one
> split and the pressure obviously in the Schur split. Now within the "primal
> variable split" a user is wondering whether we can do a further split, e.g.
> perhaps an additive split with the solid temperature split out from the
> velocities and fluid temperature (the former is almost pure conduction
> whereas the latter may be advection dominated). Is this possible?
> >
> > Alex
>
>

-- 
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https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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