Re: common nodla points on neighbouring subdomains

["Matthew Knepley" <knepley@xxxxxxxxx>]

It is unclear how you have actually mapped unknowns into your linear
system. However, a global PETSc Mat would naively have only one copy
of a given unknown, and thus the duplicate unknowns would indeed be
out of synch. You have to do extra work to communicate the values after
the solve.

However, all this is handled for you if you use the DA object. It only handles
logically Cartesian grids, but does all the ghosting. We will soon have an
unstructured counterpart.

   Matt

On 5/17/06, Thomas Geenen <geenen@xxxxxxxxx> wrote:

Dear Petsc users,

I am solving a system of equations Ax=b resulting from a Finite element
package.  The parallelization strategy for this program is to minimize
communication. therefore each subdomain has its own copy of common nodal
points between subdomains (local numbering). This strategy is already
implemented and I don't want to change that

I fill the matrix and right hand side with a call to MatSetValuesLocal and
VecSetValuesLocal. Some entries are filled on different subdomains (of course
with the same value)

The solution for the first subdomain is correct. however the solution vector
on the second subdomain does not contain the solution on the common nodal
points it shares with subdomain 1.
This is probably a feature but it is not consistent with my program setup.
The question is:
how can i tell petsc to return a solution for all the positions i filled with
VecSetValuesLocal?

Thanks in advance
Thomas Geenen
ps I got the impression that the assemble routines also exchange common nodal
point info.  It would be nice if this could be skipped as well.
Of course some extra communication could solve my problem but I would prefer a
more elegant solution if one exists

-- 
"Failure has a thousand explanations. Success doesn't need one" -- Sir Alec Guiness