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[Anders Logg <logg@xxxxxxxxx>]

On Sun, Oct 18, 2009 at 08:37:21PM +0200, Johan Hake wrote:
> On Sunday 18 October 2009 20:31:41 Garth N. Wells wrote:
> > Johan Hake wrote:
> > > On Sunday 18 October 2009 20:07:41 Garth N. Wells wrote:
> > >> On Oct 18 2009, Johan Hake wrote:
> > >>> On Sunday 18 October 2009 18:21:23 Garth N. Wells wrote:
> > >>>> Johan Hake wrote:
> > >>>>> On Sunday 18 October 2009 16:43:28 Garth N. Wells wrote:
> > >>>>>> Garth N. Wells wrote:
> > >>>>>>> Johan Hake wrote:
> > >>>>>>>> On Saturday 17 October 2009 21:08:14 Garth N. Wells wrote:
> > >>>>>>>>> Garth N. Wells wrote:
> > >>>>>>>>>> DOLFIN wrote:
> > >>>>>>>>>>> One or more new changesets pushed to the primary dolfin
> > >>>>>>>>>>> repository. A short summary of the last three changesets is
> > >>>>>>>>>>> included below.
> > >>>>>>>>>>>
> > >>>>>>>>>>> changeset:   7378:e5c921e0293a
> > >>>>>>>>>>> tag:         tip
> > >>>>>>>>>>> user:        "Johan Hake <hake@xxxxxxxxx>"
> > >>>>>>>>>>> date:        Sat Oct 17 15:45:36 2009 +0200
> > >>>>>>>>>>> files:       site-packages/dolfin/function.py
> > >>>>>>>>>>> site-packages/dolfin/functionspace.py description:
> > >>>>>>>>>>> Make Mixed FunctionSpace access more consistant.
> > >>>>>>>>>>>   - All methods are now defined in FunctionSpaceBase.
> > >>>>>>>>>>>   - We now do not save any spaces in MixedFunctionSpace
> > >>>>>>>>>>
> > >>>>>>>>>> This change broke my code. See below.
> > >>>>>>>>>
> > >>>>>>>>> Seems that the problem arises with spaces which are restricted,
> > >>>>>>>>>
> > >>>>>>>>>      V = FunctionSpace(mesh, "CG", 1, "facet")
> > >>>>>>>>
> > >>>>>>>> This is an error in the generated FFC code.
> > >>>>>>>>    ufc::finite_element::signature()
> > >>>>>>>> should return a string that can be executed in a ufl namespace and
> > >>>>>>>> then generate the corresponding ufl.FiniteElement.
> > >>>>>>>>
> > >>>>>>>> For a restricted element the signature returns:
> > >>>>>>>>
> > >>>>>>>>    "FiniteElement('Lagrange', 'triangle', 1)|_{<interval of degree
> > >>>>>>>> 1>}"
> > >>>>>>>>
> > >>>>>>>> where it should return:
> > >>>>>>>>
> > >>>>>>>>    "ElementRestriction(FiniteElement('Lagrange', Cell('triangle',
> > >>>>>>>> 1, Space(2)), 1), Cell('interval', 1, Space(1)))"
> > >>>>>>
> > >>>>>> I've had a look, and while I don't yet follow where UFL defines its
> > >>>>>> signatures,
> > >>>>>
> > >>>>>   repr(ulf_object)
> > >>>>>
> > >>>>> returns the uniqe signature of an ufl_object.
> > >>>>>
> > >>>>>> things are dangerous because FFC formats its own signature
> > >>>>>> strings, see line 227 of
> > >>>>>>
> > >>>>>>      ffc/ffc/fem/finiteelement.py
> > >>>>>
> > >>>>> Yes, this is dangerous, at least if we want to use them as we do in
> > >>>>> PyDOLFIN. However taking repr of the corresponding ufl object is a
> > >>>>> well defined method that ufl use internally, when for example
> > >>>>> creating a unique string representation of a form.
> > >>>>>
> > >>>>>> We stopped using signature strings in DOLFIN because it gave us all
> > >>>>>> sorts of problems. Is it desirable to have PyDOLFIN depend on the
> > >>>>>> generated strings? Can it be avoided?
> > >>>>>
> > >>>>> It is a very nice way of constructing an ufl object when we have the
> > >>>>> compiled version. As the convention of repr(object) is that:
> > >>>>>
> > >>>>>   new_object = eval(repr(object))
> > >>>>>
> > >>>>> should return a new object of the same kind.
> > >>>>>
> > >>>>> So when we have a SubSpace with its compiled FiniteElement, it is
> > >>>>> easy to just call its signature method of its element to generate the
> > >>>>> corresponding ufl element, which is used to construct a full fledged
> > >>>>> dolfin.FunctionSpace.
> > >>>>>
> > >>>>> Not sure how this could be done another way.
> > >>>>
> > >>>> Can't we get the sub-element from the original UFL function?
> > >>>
> > >>> Not when we return a SubSpace which is a compiled C++ structure. To be
> > >>> able to construct the ufl.FiniteElement (done in the class
> > >>> FunctionSpaceFromCpp in functionspace.py) we use the signature of the
> > >>> cpp.FiniteElement.
> > >>>
> > >>>> If I do
> > >>>>
> > >>>>     (u0, u1) = pde.solve().split()
> > >>>>
> > >>>> are u0 and u1 UFL Functions, or just cpp Functions?
> > >>>
> > >>> They should be both. Their FunctionSpaces (self._V) are constructed
> > >>> using the the FunctionSpace.sub(i) (operator[]) method, which returns
> > >>> the compiled SubSpace I am talking about above.
> > >>
> > >> OK, but if we have
> > >>
> > >>   U = pde.solve()
> > >>
> > >> and U is a UFL Function, can't the UFL finiteelement for U be accessed,
> > >> and then the UFL sub-element(s) accessed and then compiled?
> > >
> > > Yes, this should be possible! (Did not think of getting the sub element
> > > from a mixed ufl.element :P)
> > >
> > > However we do not have to compile them, as we needed to go the other way,
> > > from compiled to UFL.
> >
> > OK. Now the situation is clear to me.
> >
> > > I still think the signature() -> UFL object is a neat feature!
> >
> > The problem is that there is nothing that says that a form compiler that
> > uses UFL and produces UFC-compliant code must return the UFL signature
> > (repr) in ufc::finite_element::signature().
>
> True. However that is something we discussed a year ago when we implemented
> the transition to FunctionSpace in PyDOLFIN. I thought this went into the ufc
> documentation, but I now see that this is not the case. For now...
>
> Lets get a blueprint at ufc and here what folks says.
>
> Johan

How about adding an optional function to the UFC interface for
returning the UFL string:

  virtual std::string ufl_repr() const { return ""; }

This function can then be implemented optionally by form compilers
that rely on UFL. We should not tie the UFC interface to UFL.

--
Anders




>
>
> > Garth
> >
> > > Johan
> > >
> > >> Garth
> > >>
> > >>>>> Isn't it possible to use what repr(ufl_element) returns to define the
> > >>>>> signature of an element or isn't the ufl_element available in
> > >>>>> ffc.FiniteElement?
> > >>>>
> > >>>> Yes. I committed this change to FFC a short while ago.
> > >>>
> > >>> Ok!
> > >>>
> > >>> Johan
> > >>>
> > >>>> Garth
> > >>>>
> > >>>>> Johan
> > >>>>>
> > >>>>>>> If I look at the generated code in Poisson.h (the DOLFIN demo), the
> > >>>>>>> signature is
> > >>>>>>>
> > >>>>>>>     "FiniteElement('Lagrange', 'triangle', 1)"
> > >>>>>>>
> > >>>>>>> so the restricted one looks consistent to me. How does PyDOFLIN use
> > >>>>>>> the signature?
> > >>>>>>>
> > >>>>>>> Garth
> > >>>>>>>
> > >>>>>>>> Johan
> > >>>>>>>>
> > >>>>>>>>> Garth
> > >>>>>>>>>
> > >>>>>>>>>> Garth
> > >>>>>>>>>>
> > >>>>>>>>>>    File "solver.py", line 96, in solve
> > >>>>>>>>>>      (uhat, uu) = Uh.split()
> > >>>>>>>>>>    File
> > >>>>>>>>>> "/home/garth/code/fenics/dolfin/dolfin-all/local/lib/python2.6/s
> > >>>>>>>>>>i te- pa cka
> > >>>>>>>>>>
> > >>>>>>>>>> ges/dolfin/function.py", line 150, in split
> > >>>>>>>>>>      return tuple(self._sub(i,deepcopy) for i in
> > >>>>>>>>>> xrange(self._V.num_sub_spaces()))
> > >>>>>>>>>>    File
> > >>>>>>>>>> "/home/garth/code/fenics/dolfin/dolfin-all/local/lib/python2.6/s
> > >>>>>>>>>>i te- pa cka
> > >>>>>>>>>>
> > >>>>>>>>>> ges/dolfin/function.py", line 150, in <genexpr>
> > >>>>>>>>>>      return tuple(self._sub(i,deepcopy) for i in
> > >>>>>>>>>> xrange(self._V.num_sub_spaces()))
> > >>>>>>>>>>    File
> > >>>>>>>>>> "/home/garth/code/fenics/dolfin/dolfin-all/local/lib/python2.6/s
> > >>>>>>>>>>i te- pa cka
> > >>>>>>>>>>
> > >>>>>>>>>> ges/dolfin/function.py", line 135, in _sub
> > >>>>>>>>>>      return Function(self, i)
> > >>>>>>>>>>    File
> > >>>>>>>>>> "/home/garth/code/fenics/dolfin/dolfin-all/local/lib/python2.6/s
> > >>>>>>>>>>i te- pa cka
> > >>>>>>>>>>
> > >>>>>>>>>> ges/dolfin/function.py", line 80, in __init__
> > >>>>>>>>>>      self._V = V.sub(i)
> > >>>>>>>>>>    File
> > >>>>>>>>>> "/home/garth/code/fenics/dolfin/dolfin-all/local/lib/python2.6/s
> > >>>>>>>>>>i te- pa cka
> > >>>>>>>>>>
> > >>>>>>>>>> ges/dolfin/functionspace.py", line 88, in sub
> > >>>>>>>>>>      return FunctionSpaceFromCpp(cpp.SubSpace(self,i))
> > >>>>>>>>>>    File
> > >>>>>>>>>> "/home/garth/code/fenics/dolfin/dolfin-all/local/lib/python2.6/s
> > >>>>>>>>>>i te- pa cka
> > >>>>>>>>>>
> > >>>>>>>>>> ges/dolfin/functionspace.py", line 101, in __init__
> > >>>>>>>>>>      self._ufl_element = eval(cppV.element().signature(),
> > >>>>>>>>>> ufl.__dict__) File "<string>", line 1
> > >>>>>>>>>>      FiniteElement('Lagrange', 'triangle', 1)|_{<interval of
> > >>>>>>>>>> degree 1>}
> > >>>>>>>>>>
> > >>>>>>>>>>> changeset:   7377:40cca61143c6
> > >>>>>>>>>>> user:        "Garth N. Wells <gnw20@xxxxxxxxx>"
> > >>>>>>>>>>> date:        Sat Oct 17 13:24:47 2009 +0100
> > >>>>>>>>>>> files:       dolfin/mesh/SubDomain.h
> > >>>>>>>>>>> description:
> > >>>>>>>>>>> Small formatting fix.
> > >>>>>>>>>>>
> > >>>>>>>>>>>
> > >>>>>>>>>>> changeset:   7376:8ee974ed5f7e
> > >>>>>>>>>>> user:        Anders Logg <logg@xxxxxxxxx>
> > >>>>>>>>>>> date:        Sat Oct 17 00:05:34 2009 +0200
> > >>>>>>>>>>> files:       dolfin/function/Function.cpp
> > >>>>>>>>>>> description:
> > >>>>>>>>>>> Remove unnecessary lines in Function::eval noted by Marc S.
> > >>>>>>>>>>>
> > >>>>>>>>>>>
> > >>>>>>>>>>>
> > >>>>>>>>>>> ---------------------------------------------------------------
> > >>>>>>>>>>>- --- -- - For more details, visit
> > >>>>>>>>>>> http://www.fenics.org/hg/dolfin
> > >>>>>>>>>>> _______________________________________________ DOLFIN-dev
> > >>>>>>>>>>> mailing list DOLFIN-dev@xxxxxxxxxx
> > >>>>>>>>>>> http://www.fenics.org/mailman/listinfo/dolfin-dev
> > >>>>>>>>>>
> > >>>>>>>>>> _______________________________________________
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> > >>>>>>>>>> DOLFIN-dev@xxxxxxxxxx
> > >>>>>>>>>> http://www.fenics.org/mailman/listinfo/dolfin-dev
> > >>>>>>>>>
> > >>>>>>>>> _______________________________________________
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> >
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