[petsc-users] TS scheme with different DAs

[Matthew Knepley]

On Tue, Sep 17, 2019 at 8:27 PM Smith, Barry F. <bsmith at mcs.anl.gov> wrote:

>
>   Don't be too quick to dismiss switching to the DMStag you may find that
> it actually takes little time to convert and then you have a much less
> cumbersome process to manage the staggered grid. Take a look at
> src/dm/impls/stag/examples/tutorials/ex2.c where
>
> const PetscInt dof0 = 0, dof1 = 1,dof2 = 1; /* 1 dof on each edge and
> element center */
>     const PetscInt stencilWidth = 1;
>     ierr =
> DMStagCreate2d(PETSC_COMM_WORLD,DM_BOUNDARY_NONE,DM_BOUNDARY_NONE,7,9,PETSC_DECIDE,PETSC_DECIDE,dof0,dof1,dof2,DMSTAG_STENCIL_BOX,stencilWidth,NULL,NULL,&dmSol);CHKERRQ(ierr);
>
> BOOM, it has set up a staggered grid with 1 cell centered variable and 1
> on each edge. Adding more the cell centers, vertices, or edges is trivial.
>
>   If you want to stick to DMDA you
>
> "cheat". Depending on exactly what staggering you have you make the DMDA
> for the "smaller problem" as large as the other ones and just track zeros
> in those locations. For example if velocities are "edges" and T, S are on
> cells, make your "cells" DMDA one extra grid width wide in all three
> dimensions. You may need to be careful on the boundaries deepening on the
> types of boundary conditions.
>

Yes, SNES ex30 does exactly this. However, I still recommend looking at
DMStag. Patrick created it because managing the DMDA
became such as headache.

  Thanks,

    Matt


> > On Sep 17, 2019, at 7:04 PM, Manuel Valera via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
> >
> > Thanks Matthew, but my code is too complicated to be redone on DMStag
> now after spending a long time using DMDAs,
> >
> > Is there a way to ensure PETSc distributes several DAs in the same way?
> besides manually distributing the points,
> >
> > Thanks,
> >
> > On Tue, Sep 17, 2019 at 3:28 PM Matthew Knepley <knepley at gmail.com>
> wrote:
> > On Tue, Sep 17, 2019 at 6:15 PM Manuel Valera via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
> > Hello, petsc users,
> >
> > I have integrated the TS routines in my code, but i just noticed i
> didn't do it optimally. I was using 3 different TS objects to integrate
> velocities, temperature and salinity, and it works but only for small DTs.
> I suspect the intermediate Runge-Kutta states are unphased and this creates
> the discrepancy for broader time steps, so I need to integrate the 3
> quantities in the same routine.
> >
> > I tried to do this by using a 5 DOF distributed array for the RHS, where
> I store the velocities in the first 3 and then Temperature and Salinity in
> the rest. The problem is that I use a staggered grid and T,S are located in
> a different DA layout than the velocities. This is creating problems for me
> since I can't find a way to communicate the information from the result of
> the TS integration back to the respective DAs of each variable.
> >
> > Is there a way to communicate across DAs? or can you suggest an
> alternative solution to this problem?
> >
> > If you have a staggered discretization on a structured grid, I would
> recommend checking out DMStag.
> >
> >   Thanks,
> >
> >      MAtt
> >
> > Thanks,
> >
> >
> >
> > --
> > What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> > -- Norbert Wiener
> >
> > https://www.cse.buffalo.edu/~knepley/
>
>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

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