Hi, Roy

I am always wondering something about parallel matrix assembly and unkown variable distribution.
What relationship between global matrix obtained without parallel and matrices at nodes of the cluster with parallel. If possible, whether is there some examples or papers to demonstrate this relationship?
Whether can we directly get the global matrix without parallel using matrices at all the nodes? I think it can't,
the matrices at the nodes of the cluster are dealt with to meet the boundary problem between the nodes of the cluster. The processing is done by PETScMatrix::add_matrix()? If it is, my understanding is that this processing is algebraic and doesn't need the mesh information. PETScMatrix::add_matrix() only can know which points is on boundary between nodes. 
Is it right?

Thanks a lot.


On 2/4/08, Roy Stogner <roystgnr@ices.utexas.edu> wrote:

On Mon, 4 Feb 2008, Yujie wrote:

> thank you, Roy. To my current understanding, Ax=b should be generally
> partitioned in libmesh like:
> A11 A12 A13  x1    b1
> A21 A22 A23  x2 = b2
> A31 A32 A33  x3    b3
> if 9 processors are used. That is, there is the overlapping of x between
> different processors. if one wants to get all the
> solution, some operations are done to "combine" x in different
> processors, is it right? thanks a lot.