dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

Anders Logg wrote:
> On Wed, Dec 17, 2008 at 12:15:38AM +0000, Garth N. Wells wrote:
> > I'm running into some problems with the new Function design when trying 
> > to update a solver. I'll try to sketch the issue as simply as possible.
> >
> >      Function v;
> >      Function u, p;
> >
> >      // First form for U = (u, p)
> >      FirstBilinearForm a_1(V1, V1);
> >      FirstLinearForm   L_1(V1);
> >      LinearPDE pde_first(a_1, L_1);
> >
> >      // Second form which depends on u
> >      SecondBilinearForm a_2(V2, V2);
> >      SecondLinearForm   L_2(V2, u);
> >      LinearPDE pde_second(a_2, L_2);
> >
> >      Function U;
> >      for(uint i = 0; i < 10; ++i)
> >      {
> >        pde_first.solve(U);
> >
> >        // This step breaks down because FunctionSpaces don't match
> >        u = U[0];
> >        p = U[1];
> >
> >        pde_second.solve(v);
> >      }
> >
> > The problem is in assigning Functions since we now check the FunctionSpace.
>
> Which check is it that fails?

The check on the FunctionSpace in

    const Function& Function::operator= (const Function& v)

fails. Should we have "Function::operator=" assign a Function object, or 
just the values of a Function (as it does now)?  Also, should we have a

    const Function& operator= (const SubFunction& v);

function?

I also tried

  FunctionSpace V;
  SubSpace Vu(0);
  SubSpace Vp(1);

  Function U(V);
  Function u(Vu);
  Function p(Vp);

which doesn't work because I guess a new FunctionSpace is created for 
each SubSpace.

Should a FunctionSpace "own" its subspaces so one could do

  MyFunctionSpace V(mesh);
  FunctionSpace& sub_space V[0];

and be sure for always getting the same subspace rather than creating 
copies.


> > To get around this, I tried
> >
> >      FunctionSpace V(mesh);
> >      Function U(V);
> >      Function u = U[0];
> >      Function p = U[1];
> >
> > which throws an exception because U does not have a vector.
>
> What if we remove the check in operator[] and then in the constructor
> that gets a SubFunction we rely on v.v.vector() which (after Martin's
> fix from yesterday) will always return a vector with the dofs
> (possibly interpolated if there were no dofs before).

Yes, that would make sense if the new additions are working.

Garth

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