[petsc-users] Parallelize in the y direction

[Matthew Knepley]

On Fri, Aug 20, 2021 at 7:53 AM Joauma Marichal <
joauma.marichal at uclouvain.be> wrote:

>  Dear Sir or Madam,
>
> I am looking for advice regarding some of PETSc functionnalities. I am
> currently using PETSc to solve the Navier-Stokes equations on a 3D mesh
> decomposed over several processors.  However, until now, the processors are
> distributed along the x and z directions but not along the y one. Indeed,
> at some point in the algorithm, I must solve a tridiagonal system that
> depends only on y. Until now, I have therefore performed something like
> this:
> for(int k = cornp->zs, k<cornp->zs+cornp->zm; ++k){
>      for(int i = cornp->xs, i<cornp->xs+cornp->xm; ++i){
>            Create and solve a tridiagonal system for all the y coordinates
> (which are on the same process)
> }
> However, I would like to decompose my mesh in the y direction (as this
> should improve the code efficiency).
> I managed to do so by creating a system based on the 3D DM of all my case
> (so 1 system of size x*y*z). Unfortunately, this does not seem to be very
> efficient.
> Do you have some advice on how to cut in the y direction while still being
> able to solve x*z systems of size y? Should I create 1D DMs?
>

1) Are you using a 3D DMDA?

2) Is the coupling much different in the x and z than in the y direction?

  Thanks,

     Matt


> Thanks a lot for your help.
>
> Best regards,
>
> Joauma Marichal
>


-- 
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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