[vtkusers] read XDMF in parallel

[David E DeMarle]

I believe this is a change in the API between Xdmf2 and 3.

In Xdmf2 the VTK level reader would break up a single regular grid
automatically for you. In Xdmf3 I didn't implement that.

Workarounds include modifying your xdmf file to manually partition the
underlying hdf5 grid, or reverting to xdmf2.

Others have come across this already before. This and the new boost
dependency are the reasons why I have not yet deprecated xdmf2 and made
xdmf3 the default in VTK and ParaView. I'ld love to fix this issue, but
have not yet found the funding to devote the time for it.



David E DeMarle
Kitware, Inc.
R&D Engineer
21 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-881-4909

On Thu, Jun 18, 2015 at 3:15 PM, Nico Schlömer <nico.schloemer at gmail.com>
wrote:

> I've created a minimal working example that shows what's going wrong; find
> it attached.
>
> I'd be glad about any hints here.
>
> Cheers,
> Nico
>
>
> On Thu, Jun 18, 2015 at 8:37 PM Nico Schlömer <nico.schloemer at gmail.com>
> wrote:
>
>> It's quite the same: All nodes are on all processes. (Or so it seems:
>> `m->GetNumberOfPoints()` returns the number of all points on all nodes.)
>>
>>
>> --Nico
>>
>> On Wed, Jun 17, 2015 at 6:00 PM Berk Geveci <berk.geveci at kitware.com>
>> wrote:
>>
>>> Hi Nico,
>>>
>>> What happens if you call
>>>
>>> xreader->UpdateInformation();
>>>
>>> before you call SetUpdateExtent() ?
>>>
>>> Best,
>>> -berk
>>>
>>> On Tue, Jun 16, 2015 at 9:06 AM, Nico Schlömer <nico.schloemer at gmail.com
>>> > wrote:
>>>
>>>> From [1], I find that parallel reading of XDMF files is as simple as
>>>> ```
>>>>   vtkMPIController *contr = vtkMPIController::New();
>>>>   contr->Initialize();
>>>>   int proc = contr->GetLocalProcessId();
>>>>   int numprocs = contr->GetNumberOfProcesses();
>>>>   contr->Barrier();
>>>>   vtkXdmf3Reader *xreader = vtkXdmf3Reader::New();
>>>>   xreader->SetFileName("data/pacman.xmf");
>>>>   contr->Barrier();
>>>>   xreader->SetUpdateExtent(proc, numprocs, 0);
>>>>   xreader->Update();
>>>> ```
>>>> How can I check if this really worked?
>>>> After retrieving the output
>>>> ```
>>>>   vtkDataObject *rOutput = xreader->GetOutputDataObject(0);
>>>>   TEUCHOS_ASSERT(rOutput != nullptr);
>>>>   vtkUnstructuredGrid * m = dynamic_cast<vtkUnstructuredGrid*>(rOutput);
>>>>   TEUCHOS_ASSERT(m != nullptr);
>>>>
>>>>   std::cout << m->GetNumberOfCells() << " " << m->GetNumberOfPoints()
>>>> << std::endl;
>>>> ```
>>>> it seems that the all procs have all points and cells.
>>>>
>>>> Is there a way to only retrieve the locally owned cells/points?
>>>>
>>>> Cheers,
>>>> Nico
>>>>
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