On Sunday 18 October 2009 21:14:10 Garth N. Wells wrote: > Anders Logg wrote: > > 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 <h...@simula.no>" > >>>>>>>>>>>>>> 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.
Ok. > The really clever way would be to have PyDOLFIN create a sub-class of > ufc::finite_element which implements ufl_repr(). It is not PyDOLFIN that compile the ulf.form. This is done in the jit function of the formcompiler together with the ufc.build_module function. Not sure how easy (or correct) it is to interfere with the jit function. Johan > Garth > > > -- > > Anders > > _______________________________________________ > DOLFIN-dev mailing list > DOLFIN-dev@fenics.org > http://www.fenics.org/mailman/listinfo/dolfin-dev > _______________________________________________ DOLFIN-dev mailing list DOLFIN-dev@fenics.org http://www.fenics.org/mailman/listinfo/dolfin-dev