dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

On 20 November 2011 21:02, Anders Logg <logg@xxxxxxxxx> wrote:
> On Sun, Nov 20, 2011 at 08:40:02PM +0000, Garth N. Wells wrote:
>> On 20 November 2011 20:32, Anders Logg <logg@xxxxxxxxx> wrote:
>> > The unit test currently failing on the Mac buildbot (timing out) is
>> > failing on my machine (Ubuntu 11.10) with a PETSc error claiming that
>> > the vector in question is not ghosted.
>> >
>> > I've tracked it down to the plotting from the C++ eigenvalue demo, and
>> > the call to gather() from within interpolate_vertex_values.
>> >
>> > The problem is that the Function to be plotted is created from a
>> > solution vector x from the eigenvalue problem like so:
>> >
>> >  Function u(V, x);
>> >
>> > Since x does not come from a Function to begin with, it was not
>> > initialized with ghost values, so then later when
>> > u.interpolated_vertex_values is called, the call to gather() fails.
>> >
>> > Should there be a test for whether ghost values exist in either
>> > PETScVector or Function (_have_ghost_values)?
>> >
>>
>> Take a look here on how to test:
>>
>>     http://lists.mcs.anl.gov/pipermail/petsc-dev/2011-November/006286.html
>
> ok, so VecIsGhosted is in petsc-dev.

If you follow the thread, there is a solution for PETSc 3.2.

> It would be good to use that in
> the future but then we need the same for Epetra.
>

Epetra doesn't support ghosting - it's been added to our wrappers, so
it's easy to detect.

> But it still doesn't solve the problem with the constructor
>
>  Function u(V, x);
>
> Does it make sense in parallel when x may not have the correct
> ghosted values so calls to interpolate_vertex_values (and likely other
> functions) may fail?
>

It will be problematic when getting values from u, e.g. when used as a
coefficient. A better approach is

  Function u(V);
  *u.vector() = x; // Not sure the syntax is right

Garth

> --
> Anders
>
>
>> Garth
>>
>> > On top of this, the call to plot() does not work in parallel from C++
>> > anyway so it's easy to make the bug disappear (by moving the check in
>> > the plot function earlier to before the call to
>> > interpolate_vertex_values), but it exposes a problem with the
>> > constructor
>> >
>> >  Function u(V, x);
>> >
>> > which may not make sense if x does not have the proper layout.
>> >
>> >
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>>
>>
>>
>