dolfin team mailing list archive

[pcorreia@xxxxxxxxx]

> On Mon, Jun 11, 2007 at 01:40:50PM -0400, Harish Narayanan wrote:
>> pcorreia@xxxxxxxxx wrote:
>> > In the Stokes demo the velocity solution is written as a vtk file
>> > velocity000000.vtu.
>> > How can I plot each of the components say u and v (I use Paraview)?
>> And
>> > how to plot the vector field?
>> >
>> Assuming you've opened the file velocity.pvd in Paraview:
>>
>> 1. In order to plot the vector field, add a "glyph" from the filter menu
>> and point it to the velocity vector (U) as the data source. You can
>> change the glyph density, size, shape, etc.
>> 2. In order to plot a scalar, such as a velocity component or a norm, I
>> use the "calculator" filter. Click calculator, and you can refer to the
>> components as U_0 and U_1. So if you wanted to plot the velocity norm,
>> you'd "calculate" norm (U) and plot the result, and if you wanted to
>> just plot a component, you'd just use U_0 or U_1.
>>
>> Harish
>
> You should also be able to extract the components in DOLFIN and then
> save (or plot) each one of them:
>
>   Function u0 = u[0];
>   Function u1 = u[1];
>
> Then
>
>   plot(u0);
>   plot(u1);
>
> should plot the two components as scalar fields. Or save each one to
> VTK format if you don't have Viper.



I added this but it gives an error:

  // Solve PDE
  Function u;

  Function u0 = u[0];
  Function u1 = u[1];

  Function p;
  pde.set("PDE linear solver", "direct");
  pde.solve(u, p);

  // Plot solution
  plot(u);
  plot(p);

  plot(u0);
  plot(u1);

  // Save solution
  File ufile("velocity.xml");
  ufile << u;
  File pfile("pressure.xml");
  pfile << p;

  // Save solution in VTK format
  File ufile_pvd("velocity.pvd");
  ufile_pvd << u;
  File pfile_pvd("pressure.pvd");
  pfile_pvd << p;

  File u0_file_pvd("u.pvd");
  u0_file_pvd << u0;
  File u1_file_pvd("v.pvd");
  u1_file_pvd << u1;


$>./demo
Initializing PETSc (ignoring command-line arguments).
Creating linear PDE with 3 boundary condition(s).
terminate called after throwing an instance of 'std::runtime_error'
  what():  *** Error: Sub functions can only be extracted from discrete
functions.
p0_8737:  p4_error: interrupt SIGx: 6







>
> /Anders
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