[petsc-users] Fieldsplit with redistribute

Barry Smith bsmith at petsc.dev
Sun Apr 16 14:11:18 CDT 2023

   There is no code to do this currently. 

    I would start by building your IS for each split before the PCRedistribute and then adding to the PCApply_Redistribute() code that "fixes" these IS by "removing" the entries of the IS associated with removed degrees of freedom and then shifting the entries indices of the IS by taking into account the removed indices. But you have probably already been trying this? It does require digging directly into the PCApply_Redistribute() to get the needed information (which degrees of freedom are removed by the redistribute code), plus it requires shifting the MPI rank ownership of the entries of the IS in the same way the MPI rank ownership of the degrees of freedom of the vector are moved.

   If you have some code that you think should be doing this but doesn't work feel free to send it to us and we may be able to fix it.


> On Apr 16, 2023, at 2:50 PM, Carl-Johan Thore via petsc-users <petsc-users at mcs.anl.gov> wrote:
> Hello,
> I'm solving a blocksystem
> [A C;
> C' D],
> where D is not zero, using the PCFIELDSPLIT preconditioner and set the split using PetscFieldSplitSetIS. This works very well until I try PCREDISTRIBUTE (which is attractive as I have many locked DOFs). I suspect something goes wrong when constructing the IS for the split (I've tried various things using the IS-routines). Can PETSc do this automatically? Or else, any hints?
> Kind regards,
> Carl-Johan

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