[petsc-users] Field dependent stencil in DAs

[Matthew Knepley]

On Thu, Jul 14, 2011 at 5:31 PM, Kevin Green <Kevin.Green at uoit.ca> wrote:

>
> ________________________________________
> From: petsc-users-bounces at mcs.anl.gov [petsc-users-bounces at mcs.anl.gov] On
> Behalf Of Jed Brown [jedbrown at mcs.anl.gov]
> Sent: Monday, July 11, 2011 7:38 PM
> To: PETSc users list
> Subject: Re: [petsc-users] Field dependent stencil in DAs
>
> On Mon, Jul 11, 2011 at 18:28, Kevin Green <Kevin.Green at uoit.ca<mailto:
> Kevin.Green at uoit.ca>> wrote:
> Essentially, I'm (currently) looking to numerically solve a system of 5
> time dependent equations, but only 1 of the fields is involved with spatial
> derivatives.  Now, I've found a couple of ways to do this, either by
> introducing a Field struct cf.
> ${PETSC_DIR}/src/snes/examples/tutorials/ex19.c, or by changing one of the
> various ts examples to use DAVecGetArrayDOF(...).  Would there be any
> performance difference between introducing a Field struct compared to
> DAVecGetArrayDOF(...)?  Intuitively, I would think not...but I suppose I
> should ask since I'm here anyway.
>
> I like using field structs because then I get to use names instead of
> numbers for my fields and because there is one less level of pointer
> indirection.
>
>
> Now the real reason I came:  Is there some sort of mask that can be applied
> to the DAs that would turn off the communication of ghost points for some
> degrees of freedom?  I assume that the communication structures are set up
> so that only a single message needs to be passed between communicating
> processes on update, but this still results in passing 5X the data that I
> have to.  Any comment on this would be much appreciated.
>
> DMDASetBlockFills()
>
>
> Thank you Jed, this is exactly what I was looking for.  In the most recent
> version, it appears to be named as just DASetBlockFills().
>

Its DMDASetBlockFills() in petsc-dev, and DASetBlockFills() in petsc 3.1

   Matt

-- 
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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