Hi Andrew,

I think you should be able to use:
static void FETools::get_interpolation_matrix ( const FiniteElement< dim,
spacedim > &  *fe1*, const FiniteElement< dim, spacedim > &  *fe2*,
FullMatrix< number > &  *interpolation_matrix*  )

J-P

On 21 July 2010 15:20, Andrew McBride <[email protected]> wrote:

> hi all
>
> The finite element basis functions on the unit cell for a continuous or a
> discontinuous element should be identical if the order of the polynomial (k)
> is the same. This is, they are both in the same function space Q_k. The only
> distinction comes when one combines the elements.
>
> Would it not therefore make sense to allow the computation of the
> interpolation matrix between continuous and discontinuous finite elements if
> they derive from the same function space?
>
> At present the following code would will throw an exception (as documented)
> while I would imagine that the answer is well defined. (In the example below
> the interpolation matrix should be the identity tensor).
>
> Can one assume that the numbering of the support points for FE_Q and FE_DGQ
> elements coincides for equal order interpolation?
>
>
>    FE_Q<deal_II_dimension> fe_projection(u_degree);
>
>    FE_DGQ<deal_II_dimension> fe_projection_dg(u_degree);
>
>    FullMatrix<double> dg_to_cg_interpolation;
>    fe_projection_dg.get_interpolation_matrix(fe_projection,
> dg_to_cg_interpolation);
>
>
> An error occurred in line <358> of file
> </Users/andrewmcbride/lib/deal_svn/deal.II/deal.II/source/fe/fe_dgq.cc> in
> function
> void dealii::FE_DGQ<dim, spacedim>::get_interpolation_matrix(const
> dealii::FiniteElement<dim, spacedim>&, dealii::FullMatrix<double>&) const
> [with int dim = 3, int spacedim = 3]
> The violated condition was:
> (x_source_fe.get_name().find ("FE_DGQ<") == 0) || (dynamic_cast<const
> FE_DGQ<dim, spacedim>*>(&x_source_fe) != 0)
> The name and call sequence of the exception was:
> typename FE::ExcInterpolationNotImplemented()
> Additional Information:
> (none)
>
>
> Thanks
> Andrew
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>
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