[petsc-users] Getting DMDA local coordinates

[Åsmund Ervik]

On 21. okt. 2013 14:42, Jed Brown wrote:
> 
> The coordinates live in a different space than the DM.  Why is it
> illogical to use the coordinate DM to access coordinate vectors?  It is
> used in several examples, though none of them in Fortran.
> 

I guess it is logical for e.g. unstructured meshes or finite elements,
but for someone like me who just wants 2/4/9 real numbers, it seems a
bit overkill to have another DM.

> 
> "van der Pol" normally refers to a 2-variable ODE system (e.g.,
> src/ts/examples/tutorials/ex16.c).  I assume you are talking about a
> PDE, however.

I am actually talking about that 2-variable ODE. We use it as a test
problem in several of our codes, since it is stiff and has some
"structure", but is much simpler than Euler or Navier-Stokes. In my
example I "distribute" it so that we solve the same equation at all grid
points on all processors, using the same code as a PDE solver but with a
different RHS.

I don't know whether the pattern we use is common or not, so I'll submit
a pull request and then you can see if you think this is useful for
others. Another option would be an example solving full-blown
Navier-Stokes (single phase), but that would take some more work, and I
don't know when I'll have time for that.

Åsmund