[petsc-users] Size of off-diagonal matrix

[Jed Brown]

On Thu, Jun 23, 2011 at 14:53, John Fettig <john.fettig at gmail.com> wrote:

> I was wrong on both counts, and I still don't understand how the
> column numbering for the off-diagonal block is calculated.  It appears
> you are doing something more than just compressing the columns, you
> are also shifting the indices if an entire column is zero?
>

Yeah, that's what we mean by "compressing the columns".


>  Is there
> anyplace in the documentation that would help me understand this?
> Alternatively, where would I look in mpiaij.c?
>

The MPIAIJ format works with blocks that are in SeqAIJ format. In most
cases, it's not necessary to be familiar with the internal storage format.
Are you just curious how it's implemented, or is there something you are
trying to do that depends on the storage format?
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