[petsc-users] Question about matrix permutation

Michel Cancelliere fernandez858 at gmail.com
Fri Jan 29 11:29:02 CST 2010

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),
I realize that i cannot use block matrices because the reordering
split within the blocks and the resulting matrices are not block
matrices anymore. 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 ? not sure if it is clear


On 1/29/10, Jed Brown <jed at 59a2.org> wrote:
> On Fri, 29 Jan 2010 09:43:05 -0600 (CST), abhyshr at mcs.anl.gov wrote:
>> Instead of calling MatGetSubMatrix to get each submatrix you can use
>> MatGetSubMatrices to extract several submatrices at once. See
>> http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatGetSubMatrices.html#MatGetSubMatrices.
> I don't think Michel was asking to extract multiple matrices.  In
> serial, MatGetSubMatrices is implemented by calling MatGetSubMatrix so
> there is no weaker assumption on index set sortedness.
> Jed

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