block preconditioning questions

[Dave May]

Hi Gideon,
    I've created a small package built around petsc which contains
implementations for representing block vectors, matrices and
preconditioners. Whilst no documentation exist yet (sorry), a number of
examples are included with the package. In addition, I have only defined a
subset of operations for the block objects, but there are enough to allow
you to setup, precondition and solve both linear & nonlinear block systems.

You can obtain the tarball from within the following URL
    http://www.mcc.monash.edu.au/Codes/PetscExt

If you do try to use this package, and encounter any difficulties, please
don't hesitate to contact me.


Cheers,
    Dave May.



On Jan 8, 2008 8:19 AM, Gideon Simpson <grs2103 at columbia.edu> wrote:

> Is there a robust way to implement the following?
> Suppose I have a block diagonal matrix
> P = [A 0; 0 Q];
> and I know the indices of A and Q in this block matrix.  I now want to
> apply different preconditioners on the A block and on the Q block.
>
> One way, that I've had some success with, is to write a PCSHELL, where I
> split the input and output vectors using index sets and apply the relevant
> preconditioner on each of these.  However, this hardwires things, and I was
> wondering if there was another method.
>
>
> -gideon
>
>
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