[petsc-users] newbie question on the parallel allocation of matrices

[Treue, Frederik]

From: petsc-users-bounces at mcs.anl.gov [mailto:petsc-users-bounces at mcs.anl.gov] On Behalf Of Jed Brown
Sent: Friday, December 02, 2011 1:32 PM
To: PETSc users list
Subject: Re: [petsc-users] newbie question on the parallel allocation of matrices

On Fri, Dec 2, 2011 at 03:32, Treue, Frederik <frtr at risoe.dtu.dk<mailto:frtr at risoe.dtu.dk>> wrote:
OK, but that example seems to assume that you wish to connect only one matrix (the Jacobian) to a DA – I wish to specify many and I think I found this done in ksp ex39, is that example doing anything deprecated or will that work for me, e.g. with the various basic mat routines (matmult, matAXPY etc.) in a multiprocessor setup?

What do you mean by wanting many matrices? How do you want to use them? There is DMCreateMatrix() (misnamed DMGetMatrix() in petsc-3.2), which you can use as many times as you want.`

And this was the one I needed. However I have another question: What does DMDA_BOUNDARY_GHOSTED do, compared to DMDA_BOUNDARY_PERIODIC? From experience I now know that the PERIODIC option automagically does the right thing when I’m defining matrices so I can simply specify the same stencil at all points. Does DMDA_BOUNDARY_GHOSTED do something similar? And if so, how is it controlled, ie. How do I specify if I’ve got Neumann or Dirichlet conditions, and what order extrapolation you want, and so forth? And if not, does it then ONLY make a difference if I’m working with more than on processor, ie. If everything is sequential, is DMDA_BOUNDARY_GHOSTED and DMDA_BOUNDARY_NONE equivalent?
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