[petsc-users] Question about matrix permutation

[Jed Brown]

On Fri, 29 Jan 2010 18:29:02 +0100, Michel Cancelliere <fernandez858 at gmail.com> wrote:
> Thank you for your promptly response,  i will use unsorted inex set as
> you suggest (because my submatrices are very large (4 submatrices N/2
> x N/2 from the original one Nx N),

Wait, what are you planning to do with these submatrices?  It's likely
that PCFieldSplit can already do what you want.  Could you describe the
algorithm you want to implement?

> In terms of performance how much can affect this to the code, in the
> sense if i apply for example an ILU preconditioner to a block matrix
> (baij) and solve the same system but this time using an aij matrix ?

You have to benchmark to be sure, inodes should be used so that gives
you some of the benefits of BAIJ.  But if your algorithm is like
FieldSplit, you'll be spending time solving with the submatrices.

Jed