On Sun, Oct 18, 2009 at 09:26:11PM +0200, Johan Hake wrote: > 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
It seems better to add it to the interface so that DOLFIN can check whether the ufl_repr function is implemented or not. If it returns and empty string, then it can return an appropriate error message. -- Anders > > Garth > > > > > > _______________________________________________ > > 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
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