ffc team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

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? If I do

   (u0, u1) = pde.solve().split()

are u0 and u1 UFL Functions, or just cpp Functions?


> 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.

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
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