dolfin team mailing list archive

[Kristen Kaasbjerg <cosby@xxxxxxxxx>]

Anders Logg wrote:
> Nice. The obvious thing would be to implement this in DiscreteFunction
> and map that to the function call
>
>   virtual void Function::eval(real* values, const real* x) const;
>
> so that any Function (discrete, constant or user-defined) can be
> evaluated at an arbitrary point.
>
> It should be possible to implement this for any kind of element, and
> the code will look about the same as the code you have done for simple
> elements.
>
> We might add some kind of caching so that evaluation at multiple
> points that lie close to each other is efficient. (But maybe GTS is
> smart and handles this already.)
>
>   
ok guys, I have made a dirty hack in the C++ Function class
in order to get the desired functionality. Looks very much like
Dags code. Could I ask you to take a quick look at it (see below)
to see if I have done anything alarming. So now both the cell searching 
and the function evaluation can be done from python (and perhaps be 
condensed into one function call if desired) and it
seems to work.
Thanks for your help along the way.
Kristen

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void Function::my_eval(real* values, const real* x,
                      const ufc::cell& ufc_cell,
                      const ufc::finite_element& finite_element,
                      Cell& cell)
{
   if (!f)
       error("Function contains no data.");
   //step #1: get expansion coefficient on the cell
   uint n = finite_element.space_dimension();
   real* coefficients = new real[n];
   this->interpolate(coefficients,ufc_cell,finite_element,cell);

   //step #2: multiply with basis functions on the cell
   real* basis_val = new real[finite_element.value_dimension(0)];
   for(uint i=0; i<n; i++)
   {
       finite_element.evaluate_basis(i,basis_val,x,ufc_cell);
       values[0] += basis_val[0]*coefficients[i];
   }
}
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