On Fri, Dec 2, 2011 at 9:25 AM, Treue, Frederik <frtr at risoe.dtu.dk> wrote:
> ** ** > > ** ** > > *From:* petsc-users-bounces at mcs.anl.gov [mailto: > petsc-users-bounces at mcs.anl.gov] *On Behalf Of *Matthew Knepley > *Sent:* Friday, December 02, 2011 4:01 PM > *To:* PETSc users list > *Subject:* Re: [petsc-users] newbie question on the parallel allocation > of matrices**** > > ** ** > > On Fri, Dec 2, 2011 at 8:58 AM, Treue, Frederik <frtr at risoe.dtu.dk> wrote: > **** > > **** > > **** > > *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> 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?**** > > > GHOSTED adds extra space at the boundary so you can always use the same > stencil, but you decide what goes in there. **** > > ** ** > > Does this apply to both matrices and vectors, ie. Will the ghost points be > considered part of my computational domain or not? > The ghost nodes only exist in local vectors, not the global vectors for the solver. Matt -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20111202/2fa9fd1a/attachment.htm>
