dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Fri, Jul 04, 2008 at 11:25:52AM +0200, Martin Sandve Alnæs wrote:
> 2008/7/3 Martin Sandve Alnæs <martinal@xxxxxxxxx>:
> > 2008/7/3 Martin Sandve Alnæs <martinal@xxxxxxxxx>:
> >> I've imple
> >>
> >> 2008/7/3 Dag Lindbo <dag@xxxxxxxxxx>:
> >>> Martin Sandve Alnæs wrote:
> >>>> 2008/7/2 Dag Lindbo <dag@xxxxxxxxxx>:
> >>>>> Martin Sandve Alnæs wrote:
> >>>>>> I just added checks for valid Functions to the assembler, but this
> >>>>>> turned out to break some demos so I changed it to warnings.
> >>>>> This seems like helpful checks to make!
> >>>>>
> >>>>>> The reason is that Function(mesh, 0.0), which creates a ConstantFunction,
> >>>>>> is used for zero vector functions as well, which leaves the value shape
> >>>>>> of such a function undefined. This makes error checking impossible,
> >>>>>> which is not very nice.
> >>>>>>
> >>>>>> In my opinion, the correct next step is to keep these warnings,
> >>>>>> and turn them into errors after "a while". We should either add
> >>>>>> support for ConstantFunctions with tensor shape (would be nice),
> >>>>>> or make the demos and apps use user-define functions.
> >>>>> Adding tensor shape to the existing concept of ConstantFunction seems
> >>>>> like the way to go. IMHO, the convenience if this over user defined
> >>>>> functions is too great to discard.
> >>>>>
> >>>>> Would it not just amount to having ConstantFunction::rank() return the
> >>>>> proper value as determined by the mutable member size, instead of 0? (on
> >>>>> line 28 of ConstantFunction.cpp)
> >>>>
> >>>> No, because this size isn't known at construction time, only when
> >>>> interpolate is called with a finite_element object. A suitable (set
> >>>> of) constructor(s) needs to be defined, mirrored in Function, and
> >>>> handled in the swig interface for python.
> >>>
> >>> Yes, I see that this is needed if the rank and shape of the function is
> >>> to be set constructor. Clearly, this makes for a nice user interface! My
> >>> suggestion was more along the lines of a quick fix to get rid of the
> >>> warnings: rank() returns zero if size == 1, returns 1 if size == 2 or 3 etc.
> >>>
> >>> /Dag
> >>>
> >>>>
> >>>> // Scalar constructor
> >>>> Function f(mesh, 0.0);
> >>>>
> >>>> // General tensor constructor:
> >>>> Function f(Mesh& mesh, uint rank, uint* shape, uint* values);
> >>>>
> >>>> // vector
> >>>> uint rank = 1;
> >>>> uint shape[1] = { 2 };
> >>>> real values[2] = { 1., 2. };
> >>>> Function f(mesh, rank, shape, values);
> >>>> // or
> >>>> uint size = 2;
> >>>> real values[2] = { 1., 2. };
> >>>> Function f(mesh, 1, &size, values);
> >>>>
> >>>> // 3x3 tensor:
> >>>> uint rank = 2;
> >>>> uint shape[2] = { 3, 3 };
> >>>> real values[9] = {
> >>>>    1., 2., 3.,
> >>>>    4., 5., 6.,
> >>>>    7., 8., 9. };
> >>>> Function f(mesh, rank, shape, values);
> >>>>
> >>>
> >>>
> >>
> >> I just implemented this, but can't reproduce the old behaviour at the
> >> same time, so the demos must be updated and I guess many user
> >> applications as well. I'd like to have consensus to do this change
> >> before I continue with the demos and check in.
> >>
> >> The typical example is a zero function intended to be a vector:
> >>  Function f(mesh, 0.0);
> >>
> >> Which now would become:
> >>  uint fsize = 3;
> >>  real fvalues[3] = { 0.0, 0.0, 0.0 };
> >>  Function f(mesh, 1, &fsize, fvalues);
> >>
> >> I could evt. add a vector constructor:
> >>  real fvalues[3] = { 0.0, 0.0, 0.0 };
> >>  Function f(mesh, 3, fvalues);
> >
> > And:
> >
> >  Function f(mesh, 3, 0.0);
> >
> > which does the same as the above.
> >
> 
> I'd rather not wait a month before I merge, so I'll push these changes.
> Somebody who knows the logic should look at dolfin_function_pre.i

I think Ola knows these typemaps best.

> and fix the typemaps there, until then the python syntax for constant
> vector functions will be:
> 
> f = Function(mesh, size, array)
> 
> E.g.
> f = Function(mesh, 3, numpy.array((1.,2.,3.)))
> 
> Or simply:
> f = Function(mesh, 3, 0.0)

I think that it would be nicer to create a vector-valued function in
C++ by

  Array values(0.0, 0.0, 0.0);
  Function f(mesh, values);

and in Python by

  f = Function(mesh, [0.0, 0.0, 0.0])

-- 
Anders


> 
> Also, it would be nice if the numpy typemaps used the right numpy
> macros which converts any python sequence to the wanted format. Then
> we could use tuples instead of array above.
>

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