[petsc-dev] Using PCFieldSplitSetIS

[Dave May]

Assuming you have three IS's containing those indices (they will need
to be sorted), then you  just need to call PCFieldSplitSetIs() three
times, passing in each IS in the order you want the blocks to be
defined.

Cheers,
  Dave


On 9 March 2011 20:50, Thomas Witkowski <Thomas.Witkowski at tu-dresden.de> wrote:
> As I already asked on petsc-users, I want to implement some kind of
> iterative substructuring algorithm in my fem code. It was suggested to me to
> switch to the dev version of petsc and to make use of PCFieldSplit. So far I
> have installed petsc-dev and read a little bit about the PCFieldSplit. It
> sounds great. But I'm not really sure how to make use of. In my code I want
> to build n blocks (where n is also the number of processors), each for the
> interior domain of one rank. Okay, this seems to be easy. I make just one
> call to PCFieldSplitSetIS on each rank with IS being the global indices of
> the ranks interior nodes. But what about the n+1 block, which should contain
> all the nodes of the boundaries between the subdomains? Each rank
> contributes to this block. So how show PCFieldSplitSetIS should be called?
> May be some small example: Assume we have two ranks, each with 100 nodes in
> its interior domain and each rank contributes with 10 nodes to the interior
> boundary (so the overall interior boundary contains 20 nodes). So rank 0
> owns global indices 0 to 109, with 100 to 109 being the nodes of the first
> part of the interior boundary), and rank 1 owns global indices 110 to 219,
> with 210 to 219 being the nodes of the second part of the interior boundary.
> When I understood the idea behind PCFieldSplit correctly, it should be
> possible to generate the three blocks [0-99],[110-209],[100-109,210-219]
> using PCFieldSplitSetIs. But how to call it correctly?
>
> Thomas
>