[Trilinos-Users] [EXTERNAL] blocked problems

[Phipps, Eric T]

Hi Nico,

If possible you are better off using Thyra for this.  Thyra has much
better support for blocked operators and vectors with little memory
overhead.  You CAN use EpetraExt's block vectors for this (which is what I
use in Stokhos) but it is a pain because Epetra_Vector's don't have a
clone method.  Hence your input and output vectors for your blocked
Apply() are not necessarily block vectors themselves (but are map
equivalent to blocked vectors) and thus you have to create a view of them
as blocked vectors to get access to the blocks.  If you want to do this in
your model evaluator too, it gets even more messy to go back and forth
between the blocked and non-blocked interfaces.

-Eric

On 8/3/12 12:22 PM, "Nico Schlömer" <nico.schloemer at gmail.com> wrote:

>Hi all,
>
>I would like to extend a (let's say) linear system A by system blocks
>E=(A, B; C, D) without disturbing the circles of A (which lives in an
>EpetraExt::ModelEvaluator). Given a map mapA for and a map mapE for E,
>matrix vector multiplication Y=E*X could certainly be implemented by
>first dissecting X, copying over its entries into x, perform y=A*x,
>copy its values into Y, and do the rest of the blocks in a similar
>fashion. Since all this copying forth and back seems wasteful, I was
>wondering if there's a better alternative. In principle, there could
>be a vector/operator class stack that sticks a bunch of Epetra_Vectors
>and does the right thing for matrix-vector multiplication.
>I just looked at EpetraExt::BlockVector and friends which does sound
>promising by its name, but I can't quite get the hang of how it's
>supposed to be used. May it isn't what I want after all.
>
>Anyone with any experience here?
>
>Cheers,
>Nico
>
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