[petsc-users] working with different size of arrays in a single DA

[ilyas ilyas]

Dear Jed,


2011/4/28 Jed Brown <jed at 59a2.org>

> On Thu, Apr 28, 2011 at 13:03, ilyas ilyas <ilyascfd at gmail.com> wrote:
>
>> May be, It is a simple question, but I am little bit confused.
>> If I have two different size of arrays (one is cell-based which is from 1
>> to N,
>> other one is face-based which is from 1 to N+1).
>> How can  I create and work with them within a single DA structure,
>> for example in evaluating a function or setting up a matrix ?
>>
>
> Two choices:
>
> 1. Increase the block size (number of components per node) and just write
> the identity into the equatiosn for the "N+1" cell (which does not exist).
> This will normally give better memory performance and the few extra trivial
> equations around the margin are not a big deal.
>


Would you please explain more the first option?


>
> 2. Use two separate DAs and make the parallel decomposition compatible. You
> can put them together into one system using DMComposite. This is usually
> overkill for staggered grids, but extends to general multi-physics problems.
> Support for this option is better in petsc-dev, see, for example,
>
>
> http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-dev/src/snes/examples/tutorials/ex28.c.html
>


Thank you,
Ilyas.
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