On 12/08/2022 11:26, Matthew Knepley wrote:
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On Fri, Aug 12, 2022 at 2:21 AM Quynh Nguyen
<nguyenquynh9...@gmail.com<mailto:nguyenquynh9...@gmail.com>> wrote:
Dear petsc developers and users,
I am a new petsc user ^_^.
I have some questions about using DMDA_BOUNDARY_GHOSTED.
1. I have 2D Poisson code with domain (nx, ny), and I used DMDA_BOUNDARY_NONE,
then the size of the matrix is (nx*ny)X(nx*ny). what is the size of the matrix
if I used DMDA_BOUNDARY_GHOSTED? is it the same size as DMDA_BOUNDARY_NONE?
Yes, the matrix should be the same size, but local vectors have extra ghost
node slots.
2. if the matrix size of DMDA_BOUNDARY_GHOSTED isn't the same as
DMDA_BOUNDARY_NONE, how i can view the matrix including ghost points? I ask
this one because I used MatView(P, PETSC_VIEWER_STDOUT_WORLD) to show the
matrix but excluded ghost points.
Ghost nodes are there so that stencil operations on local vectors work at
boundaries. You fill in the slots with boundary information.
I can see how this works if you are writing your own solver but can it be used with a
KSP? In the case of periodic boundary conditions the boundary values are "filled
in" for you by PETSc. Is there any way for a user to supply boundary information to
a PETSc solver when using DMDA_BOUNDARY_GHOSTED?
Thanks,
David
Thanks,
Matt
I hope someone can explain my wonder :)
P/S: maybe, those question is simple and a bit stupid ^_^.
Have a nice day,
--
Quynh Nguyen
Graduate student, Ocean Engineering.
School of Naval Architecture and Ocean Engineering, University of Ulsan.
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