dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Wed, Apr 29, 2009 at 08:34:43AM +0200, Martin Sandve Alnæs wrote:
> On Wed, Apr 29, 2009 at 4:50 AM, Shawn Walker <walker@xxxxxxxxxxxxxxx> wrote:
> >
> >
> > On Tue, 28 Apr 2009, Anders Logg wrote:
> >
> >> On Mon, Apr 27, 2009 at 11:39:08PM -0400, Shawn Walker wrote:
> >>>
> >>>
> >>> On Mon, 27 Apr 2009, Martin Sandve Aln?s wrote:
> >>>
> >>>> On Mon, Apr 27, 2009 at 3:32 PM, Garth N. Wells <gnw20@xxxxxxxxx> wrote:
> >>>>>
> >>>>>
> >>>>> Anders Logg wrote:
> >>>>>>
> >>>>>> On Mon, Apr 27, 2009 at 09:21:58AM -0400, Shawn Walker wrote:
> >>>>>>>
> >>>>>>> On Mon, 27 Apr 2009, Anders Logg wrote:
> >>>>>>>
> >>>>>>>> On Mon, Apr 27, 2009 at 11:26:13AM +0200, Kent Andre wrote:
> >>>>>>>>>
> >>>>>>>>> On l?., 2009-04-25 at 00:14 +0200, Anders Logg wrote:
> >>>>>>>>>>
> >>>>>>>>>> On Wed, Apr 22, 2009 at 05:28:30PM -0400, Shawn Walker wrote:
> >>>>>>>>>>>
> >>>>>>>>>>> Here is the changeset that adds a `higher_order_coordinates'
> >>>>>>>>>>> variable for
> >>>>>>>>>>> storing higher order mesh data.  This is a very minor change so
> >>>>>>>>>>> please
> >>>>>>>>>>> push this.
> >>>>>>>>>>>
> >>>>>>>>>>> A changeset for DOLFIN is coming immediately after this.
> >>>>>>>>>>>
> >>>>>>>>>>> - Shawn
> >>>>>>>>>>
> >>>>>>>>>> I'm not sure what to do about this. It's problematic to add
> >>>>>>>>>> experimental work to UFC since it must be stable. In particular,
> >>>>>>>>>> any
> >>>>>>>>>> small change to ufc.h means that all forms must be recompiled
> >>>>>>>>>> everywhere for everyone.
> >>>>>>>>>>
> >>>>>>>>>> So before we make a change to UFC, we need to know exactly what we
> >>>>>>>>>> need. Which also means I can't import your DOLFIN patch since it
> >>>>>>>>>> depends on the UFC patch.
> >>>>>>>>>>
> >>>>>>>>>> I see you've added
> >>>>>>>>>>
> >>>>>>>>>>     double** higher_order_coordinates;
> >>>>>>>>>>
> >>>>>>>>>> to ufc::cell. This is analogous to what is now implemented in
> >>>>>>>>>> MeshGeometry and the mesh XML format so I think it's good.
> >>>>>>>>>>
> >>>>>>>>>> The question is what other information we need. As it works now
> >>>>>>>>>> (for
> >>>>>>>>>> the standard ufc::cell), UFC code generated by a form compiler
> >>>>>>>>>> knows
> >>>>>>>>>> what to expect from for a ufc::cell argument. If higher order
> >>>>>>>>>> mappings
> >>>>>>>>>> should work the same way, then the generated code and thus the
> >>>>>>>>>> form
> >>>>>>>>>> compilers need to know which mapping should be used and also the
> >>>>>>>>>> length of higher_order_coordinates. Is this what you were
> >>>>>>>>>> thinking?
> >>>>>>>>>>
> >>>>>>>>>> Before we do much more about it, more people need to weigh in on
> >>>>>>>>>> it as
> >>>>>>>>>> it affects DOLFIN, UFC, SyFi and FFC.
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> But is there any other way around this. It would be nice with
> >>>>>>>>> higher
> >>>>>>>>> order meshes and UFC should not stop this.
> >>>>>>>>>
> >>>>>>>>> An alternative to changing the cell class would be to make a
> >>>>>>>>> subclass
> >>>>>>>>> of cell. Would this work ?
> >>>>>>>>
> >>>>>>>> How about just using the current ufc::cell data structure as it is
> >>>>>>>> but
> >>>>>>>> let coordinates hold all the coordinates?
> >>>>>>>>
> >>>>>>>> This could also be the final solution. Then everything that's needed
> >>>>>>>> is an extra argument to tabulate_tensor that tells the generated
> >>>>>>>> code
> >>>>>>>> whether the cell is affinely mapped or not. The flag could simply be
> >>>>>>>> an integer: 1 means affine, 2 means quadratic etc.
> >>>>>>>
> >>>>>>> But you still need to modify the ufc::cell code, I think.  There is
> >>>>>>> also
> >>>>>>> an implicit assumption that the higher order coordinates should
> >>>>>>> contain
> >>>>>>> the standard mesh vertex coordinates.  Of course, this is true for
> >>>>>>> most
> >>>>>>> practical cases.  But for more fancy mappings, maybe this is not the
> >>>>>>> case.
> >>>>>>
> >>>>>> It seems to me that a reasonable assumption would be to limit the
> >>>>>> cases to P1, P2, P3, etc, that is, mappings that can be written down
> >>>>>> using standard Lagrange bases so then the vertices will always be
> >>>>>> included. They would also be first in the list meaning that the code
> >>>>>> would actually work (but might not give accurate results) even if it
> >>>>>> were generated for affine mappings.
> >>>>>>
> >>>>>>> Also, in the ufc::cell code, you currently read in the cell
> >>>>>>> coordinates
> >>>>>>> using info in MeshTopology.  However, the higher order coordinate
> >>>>>>> info
> >>>>>>> resides in MeshGeometry (which is where it belongs).  So you would
> >>>>>>> still
> >>>>>>> need to modify ufc.h.   Remember, there is higher order cell data
> >>>>>>> that is
> >>>>>>> contained in MeshGeometry.
> >>>>>>
> >>>>>> Where is MeshTopology used for this? I looked in UFCCell.h which is
> >>>>>> where the coordinates are copied to ufc::cell and there MeshGeometry
> >>>>>> is used.
> >>>>>>
> >>>>>>> Is it really that hard to change ufc.h?  Other things have to be
> >>>>>>> recompiled, but isn't that automatic?
> >>>>>>
> >>>>>> Yes, it's easy to change, but a main point with UFC is that we
> >>>>>> shouldn't change it.
> >>>>>>
> >>>>>
> >>>>> UFC will need to be extended as time goes on, but it is hard to know
> >>>>> from the outset how it should be done. What about using some IFDEF's or
> >>>>> non-pure virtual functions in the development version to allow
> >>>>> experimentation? These can then either be removed or added to UFC at
> >>>>> release time.
> >>>>>
> >>>>> Garth
> >>>>
> >>>> Or subclasses with non-pure virtual functions:
> >>>>
> >>>> class experimental_cell_integral: public ufc::cell_integral
> >>>> {
> >>>>  void foo() const { throw ...("Experimental feature not implemented.");
> >>>> }
> >>>> };
> >>>>
> >>>> or
> >>>>
> >>>> namespace eufc {
> >>>>  class cell_integral: public ufc::cell_integral
> >>>>  {
> >>>>   void foo() const { throw ...("Experimental feature not implemented.");
> >>>> }
> >>>>  };
> >>>> }
> >>>>
> >>>> We can define these in "experimental_ufc.h" or "eufc.h" to keep the
> >>>> official header file constant.
> >>>>
> >>>> Then the DOLFIN code that uses experimental features must be clearly
> >>>> marked:
> >>>>
> >>>>  ufc::cell_integral *itg = form.create_cell_integral(0)
> >>>>  eufc::cell_integral *eitg = dynamic_cast<eufc::cell_integral>(itg);
> >>>>
> >>>> and can then use "if(eitg)" to select between experimental and
> >>>> non-experimental code.
> >>>
> >>> In a similar vein, could we just have another file named eufc.h, and put
> >>> an IFNDEF somewhere that would use eufc.h instead of ufc.h?  That way I
> >>> could modify eufc.h all I want, and people don't have to use it.  But I'm
> >>> not sure how to do this.  Ideally, this would be an option for scons like
> >>> enableExpUFC=true.  Or is it only necessary to include eufc.h in files
> >>> that FFC generates?  We just need something for testing.
> >>>
> >>> Obviously, I cannot just modify UFCCell.h.  I tried that, but FFC cannot
> >>> access variables declared in the sub-class (woops...  :(  ).
> >>
> >> One option could be to create a file named ufc.h and put it in
> >>
> >>  dolfin/fem/ufc.h
> >>
> >> and change all #include <ufc.h> to #include "ufc.h".
> >>
> >> Then the DOLFIN version of ufc.h will include either the installed
> >> ufc.h or another file named ufce.h which is placed in
> >>
> >>  dolfin/fem/ufce.h
> >>
> >> That file contains data structures named the same way as in the
> >> official ufc.h but with modifications (so the rest of the code won't
> >> need to be changed much).
> >>
> >> Then in the DOLFIN ufc.h control file we place an #ifdef for whether
> >> to include the official ufc.h or the experimental one:
> >>
> >> #ifdef UFC_EXPERIMENTAL
> >> #include "ufce.h"
> >> #else
> >> #include <ufc.h>
> >> #endif
> >>
> >> You can set the flag by adding
> >>
> >>  customCxxFlags="-DUFC_EXPERIMENTAL"
> >>
> >> to scons.
> >
> > Wouldn't it make more sense to have this exp_ufc.h be a part of ufc?  That
> > way when you install ufc, there can be an `enableExpUFC' option.  In this
> > case, scons will copy exp_ufc.h to the build directory and rename it to
> > ufc.h.  The exp_ufc.h file will basically be identical to ufc.h, so it makes
> > sense to keep it together.  This will also put in a convenient `buffer' for
> > experimenting with ufc, and allow for easy moving over of additions to
> > ufc.h.  Could someone please put this in?  Please?  :)

It's better to have it in DOLFIN. It makes it easier to experiment (no
need to change UFC). When features have stabilized, we move it to UFC.

I agree having both ufc.h and UFC.h is confusing. How about this
instead. In DOLFIN, we never include ufc.h, only UFC.h. And at the top
of that file, we put

#ifdef UFC_EXPERIMENTAL
#include "ufce.h"
#else
#include <ufc.h>
#endif

That should work.

-- 
Anders

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