[petsc-users] DMDACreateSection

[Matthew Knepley]

On Wed, Apr 27, 2016 at 10:17 AM, gouarin <loic.gouarin at math.u-psud.fr>
wrote:

> Hi,
>
> I would like to know if it is possible to use DMDACreateSection to create
> a grid for Stokes problem for example using Q2-Q1 finite element
> discretization. I read old threads that tell that the implementation was
> not yet finished. And there is some comments in the code like "this is
> wrong" that tell me that it may be not available.
>
> It could be great to use DMDA like DMPlex.
>

I agree, but it was a lot of work to keep the implementation up, and I am
way behind.


> I use dmcomposite to do two grids but sections seems to be more easy to
> use and probably more efficient for the creation of the non zero structure
> of the matrix that solves the problem.
>

I have switched to just using Plex for these things, since the data in the
mesh is pretty small compared
to the solution, even if I represent the entire Cartesian grid.

I will also note that I think this is correct for the future as well since
the DMForest implementation (the
wrapper Toby Isaac wrote for p4est) uses PetscSection as well, is memory
efficient, and does structured
AMR. I am switching everything I had on DMDA to use this. If you want help
in this direction, of course
I am at your service. I am currently getting my magma dynamics code to work
in this way.

  Thanks,

     Matt


> Best,
> Loic
>



-- 
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
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