dolfin team mailing list archive

[Marie Rognes <meg@xxxxxxxxx>]

Garth N. Wells wrote:
> Marie Rognes wrote:
> > Garth N. Wells wrote:
> > > Marie Rognes wrote:
> > > > I have a slightly interesting issue, possibly with interpolate:
> > > >
> > > > Say I have a RT_0 function u. I want to interpolate this function 
> > > > onto a DG_1 function Pi_u.
> > > > Since RT_0 \subset DG_1, I would expect to get the same function. 
> > > > This does not seem
> > > > to be the case at the moment.
> > >
> > > Need to be careful interpolating in discontinuous spaces because you 
> > > will pick up the 'last' evaluated term, i.e. you can't be sure which 
> > > on side the function will be evaluated on. This could be the issue. 
> > > Have a look inside the interpolate functions in Function.cpp.
> >
> >
> > Ah. This makes the use of interpolate in errornorm pretty 
> > unpredictable ...
>
> Should be OK if u and uh are continuous.
>
> I would be inclined to remove errornorm - too much can go wrong, for 
> example, it defaults to k =3 for interpolating the exact solution and 
> what happens if uh is discontinuous.

I happen to be using errornorm a lot ;)

The main problem is with the interpolation of discontinuous functions. 
As far as I can understand, this should be mathematically possible....

Interpolate seems to interate over each cell, so the current cell is 
known. However, this information seems
to be thrown away in UFCFunction::evaluate at the call to

   void Function::eval(double* values, const Data& data) const

Wouldn't it be possible to use

   void Function::eval(double* values, const double* x, const 
ufc::cell& ufc_cell, uint cell_index) const

instead?


--
Marie