[petsc-users] petsc4py DA with dof>1 confusion

[Aron Ahmadia]

Hi Matt!

We deal with this same issue in PyClaw/PetClaw, I think Amal could do a much
better job describing the approach (or copying a relevant section from her
Master's thesis) we take to avoid copying, but the idea is to follow the
native PETSc ordering with interleaved degrees-of-freedom to keep the most
compatibility with the other DA calls.

A

On Mon, Jul 4, 2011 at 10:19 PM, Matthew Emmett <memmett at unc.edu> wrote:

> On Mon, Jul 4, 2011 at 2:52 PM, Lisandro Dalcin <dalcinl at gmail.com> wrote:
> > No, sorry... It has nothing to do with periodicity... It is actually a
> > C/Fortran ordering issue I need to fix...
>
> Ah, I see.  Thanks for looking into this so quickly.  Let me know if
> there is anything I can do on my end to help.  I will poke around the
> code for petsc4py, but you obviously know it better than I do.
>
> > In Fortran 90, it seems you index a DA Vec array as A[dof,x,y,z]... ,
> > However, I think that for Python we should follow a more C-ish
> > indexing A[x,y,z,dof]. Or we could do it like PETSc in C, that is
> > A[z,y,x,dof] (wich is the transpose of the Fortran way) but it is
> > counter-intuitive to C (and likely Python) programmers ...
> >
> > What do others think about this?
>
> I think A[x,y,z,dof] is probably the most intuitive for Python.
>
> Matt
>
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