Maybe I wasn't clear enough. I would like to completely get rid of Petsc
ordering because I don't want extra communication between processes to
construct the vector and the matrix (since I have to fill them every
time step because I'm just using the linear solver with a Mat and a Vec
data structure). I don't understand how I can do that.
My initial idea was to create another global index ordering within my
application to use only for the Petsc interface but then I think that
the ghost cells are wrong.
On 19/10/2023 14:50, Matthew Knepley wrote:
On Thu, Oct 19, 2023 at 6:51 AM Enrico <[email protected]
<mailto:[email protected]>> wrote:
Hello,
if I create an application ordering using AOCreateBasic, should I
provide the same array for const PetscInt myapp[] and const PetscInt
mypetsc[] in order to get the same ordering of the application
within PETSC?
Are you asking if the identity permutation can be constructed using the
same array twice? Yes.
And once I define the ordering so that the local vector and matrix are
defined in PETSC as in my application, how can I use it to create the
actual vector and matrix?
The vectors and matrices do not change. The AO is a permutation. You can
use it to permute
a vector into another order, or to convert on index to another.
Thanks,
Matt
Thanks in advance for the help.
Cheers,
Enrico
On 18/10/2023 13:39, Matthew Knepley wrote:
> On Wed, Oct 18, 2023 at 5:55 AM Enrico <[email protected]
<mailto:[email protected]>
> <mailto:[email protected] <mailto:[email protected]>>> wrote:
>
> Hello,
>
> I'm trying to use Petsc to solve a linear system in an
application. I'm
> using the coordinate format to define the matrix and the
vector (it
> should work better on GPU but at the moment every test is on
CPU).
> After
> the call to VecSetValuesCOO, I've noticed that the vector is
storing
> the
> data in a different way from my application. For example with two
> processes in the application
>
> process 0 owns cells 2, 3, 4
>
> process 1 owns cells 0, 1, 5
>
> But in the vector data structure of Petsc
>
> process 0 owns cells 0, 1, 2
>
> process 1 owns cells 3, 4, 5
>
> This is in principle not a big issue, but after solving the
linear
> system I get the solution vector x and I want to get the
values in the
> correct processes. Is there a way to get vector values from other
> processes or to get a mapping so that I can do it myself?
>
>
> By definition, PETSc vectors and matrices own contiguous row
blocks. If
> you want to have another,
> global ordering, we support that with
> https://petsc.org/main/manualpages/AO/
<https://petsc.org/main/manualpages/AO/>
> <https://petsc.org/main/manualpages/AO/
<https://petsc.org/main/manualpages/AO/>>
>
> Thanks,
>
> Matt
>
> Cheers,
> Enrico Degregori
>
>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which
> their experiments lead.
> -- Norbert Wiener
>
> https://www.cse.buffalo.edu/~knepley/
<https://www.cse.buffalo.edu/~knepley/>
<http://www.cse.buffalo.edu/~knepley/
<http://www.cse.buffalo.edu/~knepley/>>
--
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which
their experiments lead.
-- Norbert Wiener
https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
