ffc team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

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.

> > 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/site-
> >>>>>>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/site-
> >>>>>>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/site-
> >>>>>>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/site-
> >>>>>>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/site-
> >>>>>>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/site-
> >>>>>>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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> >>>>>
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