dolfin team mailing list archive

[Johan Jansson <jjan@xxxxxxxxxxx>]

On Tue, Sep 19, 2006 at 03:50:21PM +0200, Anders Logg wrote:
> On Tue, Sep 19, 2006 at 12:43:00PM +0200, Johan Jansson wrote:
> It looks a little strange:
> 
> void Function::interpolate(Function& ftarget)
> {
>   // Delegate function call
>   f->interpolate(ftarget);
> }
> 
> Here ftarget is the target for the interpolation, so ftarget = P(*this).
> 
> But then in DiscreteFunction::interpolate()
> 
> void DiscreteFunction::interpolate(Function& fsource)
> {                                             ~~~~~~
>   Vector& x = vector();
>               ~~~~~~~~~
>   ...
>       x(nodes[i]) = coefficients[i];
>       ~~~~~~~~~~~~~
> }
> 
> So it seems that ftarget is actually the source.
> 

This is fixed now, I changed my mind mid-way.

> > I want to add projection too, but that probably has to go via
> > PyDOLFIN.
> 
> It seems that this will only work when the old interpolate() function
> works, and that one only works when interpolating onto a restriction
> of the global space. It won't work between different types of
> functions defined by different elements or on different meshes.

You're right. I guess global interpolation is not defined between
general finite elements. So projection is a better way to go, probably
also for the case of different meshes.

> Another thing: do you need to do the interpolation from initial values
> explicitly? I made a fix previously so you can define say u0 as a
> user function, but then you can do
> 
>   u0 = u1;
> 
> and u0 becomes a discrete function. Then the interpolation is not needed.
> 

I don't think this mechanism is sufficient. In general I want to evaluate:

dot(u) = f(u)

where u could be composed of several subfunctions. Currently the
administration of the layout of the subfunctions is done manually, but
this can likely be solved with the subelement/subfunction interface in
the future. Currently I need to assume u is a DiscreteFunction, and it
will be hard to write f(u) if I have to take into account that u can
suddenly change from being a UserFunction to a DiscreteFunction.

  Johan