Comment 7 for bug 1088175

On Tue, Dec 11, 2012 at 11:21 PM, Anders Logg <email address hidden> wrote:
> On Sun, Dec 09, 2012 at 04:02:03PM +0100, Anders Logg wrote:
>> On Sun, Dec 09, 2012 at 02:32:19PM -0000, Garth Wells wrote:
>> > On Sun, Dec 9, 2012 at 2:01 PM, Anders Logg <email address hidden> wrote:
>> > > On Sun, Dec 09, 2012 at 01:27:50PM -0000, Garth Wells wrote:
>> > >> On Sun, Dec 9, 2012 at 1:20 PM, Anders Logg <email address hidden> wrote:
>> > >> > I can take a look but object to the description. It is indeed written
>> > >> > to work in parallel. It has also been tested to work in parallel
>> > >> > before.
>> > >> >
>> > >>
>> > >> Tested where?
>> > >
>> > > I thought the unit test was running fine on the buildbots but I see
>> > > now it was never added to the list of tests (in the main test.py).
>> > >
>> >
>> > The unit test is a special case for which it may run on 3 processes
>> > because the number of dofs is divisible by 3. In general, the parallel
>> > layouts will not match.
>>
>> It doesn't even work for that case. So what happened is that I thought
>> the test was run on the buildbot and therefore worked in parallel. I
>> see now why it doesn't work but it should be relatively easy to fix.
>
> I've made an attempt to fix this but it still crashes.

If you're using test/unit/la/python/LinearOperator.py to test, the line:

    b = Vector(V.dim())

will certainly cause a problem. We have the function
GenericMatrix::.resize(GenericVector&x, std::size_t dim) to re-size a
vector consistently with a matrix operator,

Garth

> I'm
> initializing the local range for the mat shell matrix using the same
> local range as for the solution vector:
>
> // Get local range
> std::size_t m_local = M;
> std::size_t n_local = N;
> if (MPI::num_processes() > 1)
> {
> std::pair<std::size_t, std::size_t> local_range = x.local_range();
> m_local = local_range.first;
> n_local = local_range.second;
> }
>
> // Initialize PETSc matrix
> A.reset(new Mat, PETScMatrixDeleter());
> MatCreateShell(PETSC_COMM_WORLD, m_local, n_local, M, N, (void*) this, A.get());
> MatShellSetOperation(*A, MATOP_MULT, (void (*)()) usermult);
>
> What am I missing? Does the solution vector not have the same parallel
> layout as the right-hand side b (which gets multiplied by the matrix
> in the Krylov solver)?
>
> --
> Anders
>
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> https://bugs.launchpad.net/bugs/1088175
>
> Title:
> LinearOperator does not work in parallel
>
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