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

[Aron Ahmadia]

Matt,

Also, in case you are looking for an example of how it is done in PyClaw:

https://github.com/clawpack/pyclaw/tree/master/apps/shallow/2d

Shallow-water is not one of the automatically verified examples, but we'll
be happy to help you if you have any questions about the code.

A

On Mon, Jul 4, 2011 at 10:48 PM, Matthew Emmett <memmett at unc.edu> wrote:

> Hey Aaron,
>
> Thanks for the tip!  I'll play around with the indexing and reshaping.
>
> Matt
>
> On Mon, Jul 4, 2011 at 3:33 PM, Aron Ahmadia <aron.ahmadia at kaust.edu.sa>
> wrote:
> > 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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