dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Mon, Feb 13, 2006 at 06:07:34PM +0100, Garth N. Wells wrote:
> On Mon, 2006-02-13 at 10:53 -0600, Anders Logg wrote:
> 
> > ok, let's begin with fixing the XML input/output for Vector. 
> 
> Sounds good.
> 
> 
> > Then we
> > should have what we need to read/write functions + we also need to
> > decide on which elements to precompile and store.
> > 
> > The XML format for Vector is temporarily disabled after the change of
> > linear algebra backend to PETSc, so it should be easy to fix.
> > 
> > There's a lot of different elements we would potentially need to
> > pregenerate, including different degree polynomials, vector-valued
> > elements with different number of components, mixed elements etc, so
> > it's not obvious which we should pick. (Of course if something is
> > missing in the first set of elements we can always add it later when
> > someone needs it.)
> 
> I would consider leaving this up to the user because of the huge number
> of elements that this could lead to.

So the user would have to supply the element? Something like

     Function u;
     File file("solution.xml");
     file >> u;
     u.attach(element);

or

     Function u(element);
     File file("solution.xml");
     file >> u;

What about the mesh? Perhaps it should also be possible to specify the
mesh so it can be shared between several Functions:

     Function u(mesh, element);
     File file("solution.xml");
     file >> u;

or perhaps that's not necessary since one can always just save the
vector:

     Function u;
     File file("solutionvector.xml");
     file >> u.vector();

/Anders
     
> >  
> > > 
> > > > > > 2. An interface for projecting/interpolating between Functions. The
> > > > > > main example which requires some manual work in solvers is defining
> > > > > > the initial values by a UserFunction and wanting to represent that as
> > > > > > a DiscreteFunction.
> > > > > 
> > > > > I'm not sure what you mean. I thought I solved this with the new
> > > > > functionality I added to the Function class last week. You can define
> > > > > a Function for the initial value by overloading eval(), or even by
> > > > > 
> > > > > Function u = 0.0;
> > > > > 
> > > > > and then u can change from being a user-defined Function to a discrete
> > > > > Function. See new convection-diffusion demo.
> > > > > 
> > > > > You can also do
> > > > > 
> > > > > Function u(x, mesh, element);
> > > > > u = f;
> > > > > 
> > > > > to interpolate f to u.
> > > > > 
> > > > 
> > > Is the interpolation linear (to the vertexes only), or does it work for
> > > higher-order elements?
> > 
> > Works for all types of elements. The function f is evaluated at all
> > nodes of the element that defines u.
> > 
> Great!
> 
> Garth
> 
> > /Anders
> > 
> > > Garth
> > > 
> > > > Ok, great! I'm sorry, I didn't realize this was what you added last
> > > > week.
> > > > 
> > > > I think interpolation is enough, projection can wait.
> > > > 
> > > > > I have limited time to work on new features before Geilo, but I can
> > > > > probably fit something in if I get some help.
> > > > > 
> > > > 
> > > > Yes, I also have limited time. But maybe we can at least start looking
> > > > at Function input and decide what we should do, i.e. if we should
> > > > design a DOLFIN XML data format for Functions or use the VTK format.
> > > > 
> > > >   Johan
> > > > 
> > > > _______________________________________________
> > > > DOLFIN-dev mailing list
> > > > DOLFIN-dev@xxxxxxxxxx
> > > > http://www.fenics.org/cgi-bin/mailman/listinfo/dolfin-dev
> > 
> 
> 
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-- 
Anders Logg
Research Assistant Professor
Toyota Technological Institute at Chicago
http://www.tti-c.org/logg/