[Trilinos-Users] Defining bordered problems efficiently: Epetra_Import

Daniele Avitabile d.avitabile at gmail.com
Mon Nov 24 05:53:24 MST 2008

Hi everybody,

the solution to the PDEs I am solving is stored in an Epetra_Vector x, based
on a certain linear Epetra_Map xMap. Now, I need to add an extra ODE to my
system, defined on the boundary. At the present stage, whenever I want to
compute the right-hand side of my PDE, I need to access a new "bordered"
Epetra_Vector xExt, based on a new map Epetra_Map xExtMap.

The problem is that, from each processor, I need access to the last
component of xExt, the one on the boundary.

The way I am doing this is
1. define an Epetra_Map overlappedXExtMap. All the GID of xExtMap are also
contained in overlappedXExtMap, plus the last component of xExt is
replicated on all processors.
2. define an importer with xExtMap as source and overlappedXExtMap as target
3. each time I evaluate the right-hand side of my equation, use the

I rely on the importer massively, because I also use it for printing
purposes: I want to separate the solution in the interior of my PDE from the
additional scalar component on the boundary.

My questions:
a. do you have a more efficient way to do this? It seems to me that I am
copying a lot of unnecessary data, namely all the components relative to the
GID of xEtxMap that are also in overlappedXExtMap.
b. how does the importer Work? Does he really copy all the elements?

Thanks in advance.

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