dolfin team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

On Tuesday 04 November 2008 13:15:51 Anders Logg wrote:
> On Mon, Nov 03, 2008 at 10:38:40PM +0100, Anders Logg wrote:
> > On Mon, Nov 03, 2008 at 06:25:18PM +0100, Martin Sandve Alnæs wrote:
> > > 2008/11/3 Anders Logg <logg@xxxxxxxxx>:
> > > > On Mon, Nov 03, 2008 at 03:55:31PM +0000, Garth N. Wells wrote:
> > > >> Anders Logg wrote:
> > > >> > On Mon, Nov 03, 2008 at 02:38:36PM +0000, Garth N. Wells wrote:
> > > >> >> Anders Logg wrote:
> > > >> >>> On Mon, Nov 03, 2008 at 11:22:26AM +0000, Garth N. Wells wrote:
> > > >> >>>> Anders Logg wrote:
> > > >> >>>>> On Sun, Nov 02, 2008 at 06:29:25PM +0000, Garth N. Wells wrote:
> > > >> >>>>>> Anders Logg wrote:
> > > >> >>>>>>> On Sun, Nov 02, 2008 at 05:52:21PM +0000, Garth N. Wells 
wrote:
> > > >> >>>>>>>> Do we want to insist that Dirichlet bc functions that do
> > > >> >>>>>>>> not appear inside a form are constructed with a
> > > >> >>>>>>>> FunctionSpace? DirichletBC is supplied with a
> > > >> >>>>>>>> FunctionSpace, so if the bc Function does not have a
> > > >> >>>>>>>> FunctionSpace, we could attach one automatically.
> > > >> >>>>>>>>
> > > >> >>>>>>>> Garth
> > > >> >>>>>>>> _______________________________________________
> > > >> >>>>>>>> DOLFIN-dev mailing list
> > > >> >>>>>>>> DOLFIN-dev@xxxxxxxxxx
> > > >> >>>>>>>> http://www.fenics.org/mailman/listinfo/dolfin-dev
> > > >> >>>>>>>
> > > >> >>>>>>> I think this is already handled. Look in the Poisson demo.
> > > >> >>>>>>> It uses a Constant to set the BC and it does not have a
> > > >> >>>>>>> FunctionSpace attached to it. The DirichletBC class now uses
> > > >> >>>>>>> its own FunctionSpace rather than the one that the Function
> > > >> >>>>>>> has (if any). There is a check (in DirichletBC::check())
> > > >> >>>>>>> that checks that the FunctionSpace for the Function is the
> > > >> >>>>>>> same as the one in the DirichletBC.
> > > >> >>>>>>
> > > >> >>>>>> It works for Constant, but not for Functions. I was getting
> > > >> >>>>>> an error when Function::interpolate is called.
> > > >> >>>>>> Function::interpolate leads to eval being called, in which
> > > >> >>>>>> case there is a test for the FunctionSpace which fails.
> > > >> >>>>>> Constant provides its own eval and therefore doesn't have a
> > > >> >>>>>> problem.
> > > >> >>>>>>
> > > >> >>>>>> For now, I've added a test in DirichletBC for the
> > > >> >>>>>> FunctionSpace. What we can add is an attach function if there
> > > >> >>>>>> is no FunctionSpace associated.
> > > >> >>>>>>
> > > >> >>>>>> Garth
> > > >> >>>>>
> > > >> >>>>> In which demo does this show up? Is there a simple way I can
> > > >> >>>>> comment something out to reproduce the error so I understand
> > > >> >>>>> what goes wrong?
> > > >> >>>>
> > > >> >>>> Look at /demo/nls/nonlinearpoisson/cpp.
> > > >> >>>>
> > > >> >>>> If you change
> > > >> >>>>
> > > >> >>>>    DirichletBoundaryCondition g(V, t);
> > > >> >>>>
> > > >> >>>> to
> > > >> >>>>
> > > >> >>>>    DirichletBoundaryCondition g(t);
> > > >> >>>>
> > > >> >>>> it will break down.
> > > >> >>>>
> > > >> >>>> Garth
> > > >> >>>
> > > >> >>> ok I see the problem now.
> > > >> >>>
> > > >> >>> The problem is a user may choose to either overload a scalar
> > > >> >>> eval function or a tensor eval function and we need to decide
> > > >> >>> which one after the callback from ufc::function::evaluate(). If
> > > >> >>> the FunctionSpace is not known, we can't decide which one to
> > > >> >>> pick.
> > > >> >>>
> > > >> >>> If we insist that one should be able to pass a Function without
> > > >> >>> a FunctionSpace to a DirichletBC, then we must remove the scalar
> > > >> >>> eval function.
> > > >> >>
> > > >> >> Fine with me. I think that it makes things simpler because the
> > > >> >> eval interface remains the same for all user-defined functions.
> > > >> >>
> > > >> >> Garth
> > > >> >
> > > >> > ok. It will also look the same as in Python.
> > > >>
> > > >> We discussed recently passing an object to eval() which contains
> > > >> some data. It would be useful the object also carried information on
> > > >> the rank and dimension of the function to allow checks and switching
> > > >> between 1D/2D/3D problems.
> > > >>
> > > >> Garth
> > > >
> > > > Yes, this would be nice, but it won't work as long as we don't
> > > > require that a Function always has a FunctionSpace. We could add some
> > > > new classes to handle error checking and data for user-defined
> > > > Functions:
> > > >
> > > >  void eval(Values& values, Data& data)
> > > >  {
> > > >    values[0] = sin(data.x[0]);
> > > >  }
> > > >
> > > > The class Values could check that data is not assigned to any illegal
> > > > indices and it could also check that all values have been assigned
> > > > etc, but if the Function does not know its FunctionSpace, this can't
> > > > be done.
> > > >
> > > > Another complication related to this but also to the thread-safety of
> > > > cell() and facet() is that UFC gets in the middle of the call
> > > > sequence:
> > > >
> > > >  assemble()
> > > >
> > > >  |--> Function::interpolate()
> > > >  |
> > > >       |--> FiniteElement::evaluate_dof()
> > > >       |
> > > >            |--> ufc::finite_element::evaluate_dof
> > > >            |
> > > >                 |--> ufc::function::evaluate()
> > > >                 |
> > > >                      |--> Function::eval()
> > > >
> > > > Since eval() is called from the generated UFC code, any arguments
> > > > like cell and facet passed from the assembler will be lost on the
> > > > way.
> > > >
> > > > Should we extend the UFC interface to allow sending a void* to
> > > > evaluate_dof which it will propagate to evaluate()?
> > >
> > > That's possible, but not very safe.
> > >
> > > A typesafe alternative is that dolfin::Function doesn't inherit
> > > ufc::function, but a ufc::function subclass is created which has a
> > > dolfin::Function which it calls and a dolfin::Data & which it sends in
> > > the call. Then we avoid ufc complications in dolfin::Function, and one
> > > such wrapper function can be created for each thread.
> > > It doesn't really add any more function calls, since it replaces the
> > > existing ufc::function::evaluate in the call stack you wrote above.
> >
> > Sounds good. I'll try something like this.
>
> This is now implemented. Take a look in Function::interpolate(),

Should it be called FunctionData instead? 

As Data is implemented now it cannot be changed after creation, i.e., you 
cannot set _facet or _cell. Would it be benefitial to cache the Data object 
and the dofs, which both are created for each call of interpolate?

Johan