[petsc-users] overset grids

[Mark Cunningham]

As a novice PETSc user, can I ask for some advice? I've found some test
examples that do similar sorts of things but I would appreciate any
suggestions.
I have a matrix generated from overset meshes with a structure like
A = |A0  B01     B0n|
      |B01  A1     B1n|
         :                 :
      |B0n    ...        An|   where the Ai are finite difference stencils
and the Bij
 represent interpolation between the grids.
1. If I create a DMDA composite object that defines each of the grid sizes
through repeated calls to DMCreate1D (because we are omitting blanked
points from the 3D mesh) and create the matrix
through DMCreateMatrix, can I still fill the matrix through MatSetValues
using the global index?
(This is how the code operates now.)
2. If I have to declare the matrix to be matnest and I have to create each
of the subblocks individually, how do I cope with some of the Bij being all
zero? Must there be a MatSetValues call for each block?
3. The principle reason at the moment for the change is to use
diag(A0...An) as the precondition matrix and use ILU on the blocks. If I
set the preconditioner to be bjacobi and then fetch the subksps, can I then
set the subpcs to be ilu?
4. A further complication is we would like to have a boundary condition
where the values of the boundary points are defined by an expansion in
functions that satisfy the radiation condition.  So, I would like to define
an index set that identifies the boundary points and define a PCSHELL on A
that for the pcsetup phase will do a QR factorization of the auxiliary
matrix: G, where we're solving
Gy = QRy =c and then on pcapply do the Ry = Q* c triangular solve that will
enable me to update
the boundary points (y subset of x the solution vector.)  How do I get the
PCSHELL to work with the block jacobi strategy.

Thanks for any suggestions.

Mark Cunningham
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20200124/2a2b3362/attachment.html>