ffc team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

Rob is at a conference, so I will go ahead and apply your patch (the
one-line fix) to the CVS version of FIAT. (And if I do it within the next
minute, it will make the 10 o'clock tar-ball...)

/Anders

On Tue, Jul 12, 2005 at 01:24:25PM +0200, Garth N. Wells wrote:
> Hi Johan,
> 
> I ran into this problem with FIAT when defining a discontinuous constant scalar
> basis function in ffc (the vector version works). I sent an email with a patch
> to the FIAT-dev list about this. Below is what I have, which multiplies the
> masss matrix by the element length (just for testing) and seems to work well now.
> 
> 
> scalar       = FiniteElement("Lagrange", "triangle", 1)
> vector       = FiniteElement("Vector Lagrange", "triangle", 1)
> scalar_const = FiniteElement("Discontinuous Lagrange", "triangle", 0)
> 
> v  = BasisFunction(scalar)     # test function
> u  = BasisFunction(scalar)     # trial function
> f  = Function(scalar)          # source term
> h  = Function(scalar_const)    # element size h
> 
> a = h*v*u*dx 
> L = v*f*dx
> 
> Then, following Anders's advice, I set up a function
> 
> Vector hvector;
> hvector.init(mesh.noCells());
> for (CellIterator cell(mesh); !cell.end(); ++cell)
> {
>   hvector((*cell).id()) = sqrt(2*(*cell).volume());
> }
> Function h(hvector);
> 
> 
> Garth
> 
> 
> Quoting jhoffman@xxxxxxxxxxx:
> 
> > Hi Anders,
> > 
> > I have started to look at how to solve the stabilization problem in the
> > best way. I first tried the approach with a piecewise constant function
> > for the stabilization parameter, but I seem to have missed something? Do
> > you find anything obvious wrong with the form-file below?
> > 
> > /Johan
> > 
> > 
> > name = "NSEContinuity"
> > scalar_element = FiniteElement("Lagrange", "tetrahedron", 1)
> > vector_element = FiniteElement("Vector Lagrange", "tetrahedron", 1)
> > disc_scalar_element = FiniteElement("Discontinuous Lagrange",
> > "tetrahedron", 0)
> > 
> > q = BasisFunction(scalar_element)
> > p = BasisFunction(scalar_element)
> > uc = Function(vector_element)
> > f = Function(vector_element)
> > d1 = Function(disc_scalar_element)
> > 
> > i0 = Index()
> > i1 = Index()
> > i2 = Index()
> > 
> > a = q.dx(i0)*p.dx(i0)*dx
> > L = q.dx(i0)*f[i0]*dx - q.dx(i0)*uc[i1]*uc[i0].dx(i1)*dx -
> > (1/d1)*q*uc[i0].dx(i0)*dx
> > 
> > 
> > 
> > 
> > skalman:~/local> ffc NSEContinuity.form
> > This is FFC, the FEniCS Form Compiler, version 0.1.8.
> > For further information, go to http://www/fenics.org/ffc/.
> > 
> > Parsing NSEContinuity.form
> > Output written to NSEContinuity.py
> > [[((-1.0, -1.0, -1.0),), ((1.0, -1.0, -1.0),), ((-1.0, 1.0, -1.0),),
> > ((-1.0, -1.0, 1.0),)], [(), (), (), (), (), ()], [(), (), (), ()], [()]]
> > ((-1.0, -1.0, -1.0), (1.0, -1.0, -1.0), (-1.0, 1.0, -1.0), (-1.0, -1.0,
> > 1.0))
> > Warning: element untested
> > Traceback (most recent call last):
> >   File "/usr/bin/ffc", line 81, in ?
> >     main(sys.argv[1:])
> >   File "/usr/bin/ffc", line 59, in main
> >     execfile(outname)
> >   File "NSEContinuity.py", line 32, in ?
> >     disc_scalar_element = FiniteElement("Discontinuous Lagrange",
> > "tetrahedron", 0)
> >   File "/home/hoffman/local/lib/python/ffc/compiler/finiteelement.py",
> > line 66, in __init__
> >     self.element = DiscontinuousLagrange(fiat_shape, degree)
> >   File "/home/hoffman/local/lib/python/FIAT/DiscontinuousLagrange.py",
> > line 87, in DiscontinuousLagrange
> >     if n == 0: return P0.P0( shape )
> >   File "/home/hoffman/local/lib/python/FIAT/P0.py", line 35, in __init__
> >     Udual = P0Dual( shape , U )
> >   File "/home/hoffman/local/lib/python/FIAT/P0.py", line 21, in __init__
> >     d = shapes_new.dims[ shape ]
> > AttributeError: 'module' object has no attribute 'dims'
> > 
> > 
> > 
> > 
> > 
> > 
> > > On Fri, Jul 08, 2005 at 11:02:04PM +0200, Garth N. Wells wrote:
> > >> Hi Anders,
> > >>
> > >> I'm trying to stabilise a problem and for this I need a measure of the
> > >> element
> > >> area. Do you have any plans to make this sort of information available
> > >> through
> > >> ffc? I have seen that Johan H. hasn't yet defined the element length in
> > >> the
> > >> Navier-Stokes module yet. Johan, do you have a plan how to do this? It
> > >> could be
> > >> done easily by defining a constant in the .form file and then adding a
> > >> line c4 =
> > >> sqrt(det), but this would destroy the beauty of the ffc generated file.
> > >
> > > I will probably add a default Function h(x) that gives you the size of
> > > the element. Do you need the side length (diameter) or the area?
> > >
> > > This will probably not be until after the summer though, so what you
> > > can do now is to define a piecewise constant function that is defined
> > > as the mesh size or area or whatever, like so:
> > >
> > >    P0 = FiniteElement("Discontinuous Lagrange", "triangle", 0)
> > >    h  = Function(P0)
> > >
> > > and then define a corresponding Function in DOLFIN from a Vector and
> > > set the values of the Vector to the local mesh size (x(i) area of
> > > triangle i).
> > >
> > >> A more general question - do you have a plan on how more complicated
> > >> nonlinear
> > >> problems, such as plasticity, will fit in with ffc + DOLFIN? I mean here
> > >> solving
> > >> equations in which the coefficients of an equation themselves come from
> > >> the
> > >> solution of a non-trivial nonlinear problem, such a plasticity return
> > >> mapping
> > >> algorithm.
> > >>
> > >> Garth
> > >
> > > This is already implemented. When you define a Function in FFC, then
> > > this corresponds to a Function in DOLFIN, and the DOLFIN Function
> > > could be either defined by an expression or it can be the solution of
> > > another problem.
> > >
> > > The Function concept is really central to both FFC and DOLFIN, and it
> > > is the key to working with FFC and DOLFIN. Each Function in FFC
> > > corresponds to a Function in DOLFIN, and it should not matter how the
> > > Function is defined in DOLFIN. There are a couple of things missing,
> > > like reading Functions from file, projection between different
> > > function spaces, but the basic stuff is implemented. (Take a look at
> > > Function.cpp, it's pretty short.)
> > >
> > > Ask again if something is unclear.
> > >
> > > /Anders
> > >
> > > _______________________________________________
> > > FFC-dev mailing list
> > > FFC-dev@xxxxxxxxxx
> > > http://www.fenics.org/cgi-bin/mailman/listinfo/ffc-dev
> > >
> > 
> > 
> > 
> > _______________________________________________
> > FFC-dev mailing list
> > FFC-dev@xxxxxxxxxx
> > http://www.fenics.org/cgi-bin/mailman/listinfo/ffc-dev
> > 
> 
> _______________________________________________
> FFC-dev mailing list
> FFC-dev@xxxxxxxxxx
> http://www.fenics.org/cgi-bin/mailman/listinfo/ffc-dev
> 

-- 
Anders Logg
Research Assistant Professor
Toyota Technological Institute at Chicago
http://www.tti-c.org/logg/