[petsc-users] Assembly of local Mat's to a parallel Mat

[Matthew Knepley]

On Fri, Apr 12, 2013 at 11:49 AM, Hui Zhang <mike.hui.zhang at hotmail.com>wrote:

>
> On Apr 12, 2013, at 5:22 PM, Jed Brown wrote:
>
> > Hui Zhang <mike.hui.zhang at hotmail.com> writes:
> >
> >> Assembly it directly. I just found MatGetSubMatricesParallel.
> >
> > This is not a private implementation function so it's not a good place
> > to learn.  It also doesn't do what you want.
> >
> > For your purpose, you can either loop over the entries of A_i inserting
> > them according to the R_i
>
> I can understand this method.  A further question: since Ai itself is
> shared
> by many processors,  MatSetValues to A should be called by only one of the
> processor sharing Ai.  Is it right?
>

MatSetValues() is not collective.


> > or you can create a block diagonal parallel
> > matrix A_i constructed by joining together all the diagonal blocks.
>
> Which function can do this?  I only found diagonal block Mat with each
> block
> of the same size and dense.  Thanks!
>

This is just a simple shift in index with normal MatSetValues().

   Matt


> > Presumably R is already parallel, so then you can use MatPtAP to
> > assemble the product.
> >
> > Note that you might be able to assemble the block diagonal A directly.
> >
> >> Maybe I can learn from the source codes of this function but I can not
> >> find where they are.
> >
> > For navigating source code, see the manual section about setting up GNU
> > Global tags or etags.  PETSc functions are named to tab complete well
> > with tags.
> >
>
>


-- 
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
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