[petsc-users] Equivalent of VecScatter for index sets

[Rémi Lacroix]

Le 13/01/2014 19:00, Matthew Knepley a écrit :
> On Mon, Jan 13, 2014 at 9:47 AM, Rémi Lacroix <remi.lacroix at inria.fr 
> <mailto:remi.lacroix at inria.fr>> wrote:
>
>     Hello,
>
>     I would like to permute an index set with another index set, just
>     like you can do for vectors using VecScatter.
>
>     I have two index sets IS1 and IS2 which share the same size but
>     have different parallel layouts. I often need to permute
>     vectors/matrices using those two index sets (as in first permute
>     with IS1 then permute the result with IS2). Since I don't use the
>     intermediate result, I would like to permute IS1 with IS2 to get a
>     new index set so that I can permute directly my vectors/matrices
>     with it. Is that possible using Petsc?
>
>
> We do not have this particular composition in our interface. However, 
> you could accomplish this using PetscSF.
>
>   Thanks,
>
>      Matt

Thanks for the quick answer.

So basically I need to have a look at the underlying mechanism of 
VecScatter and implement something similar for IS. How complex would it 
be in practice?

Rémi
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