Start with a brute force approach:
FE_Q<dim> fe(degree);
QGaussLobatto<dim> quad(degree+1);
const std::vector<Point<dim> > &q = fe.get_unit_support_points()
std::vector<double> w(q.size());
tol = 1e-10;
// check everything is fine
AssertDimension(w.size(), quad.size());
for(unsigned int i=0; i<q.size(); ++i) {
w[i] = -1.0;
for(unsigned int j=0; j<q.size(); ++j) {
if( q[i].distance(quad.point(j)) < tol ) {
w[i] = q.weigth(j);
break;
}
Assert(w[i] == -1.0, ExcInternalError(“Did not find the point!”));
}
Quadrature<dim> new_quad(q,w);
Now you are sure that the quadrature new_quad is doing what you asked for.
L.
> On 23 Nov 2016, at 11:04, Praveen C <[email protected]> wrote:
>
> Thanks Luca.
>
> I needed this property to efficiently implement a spectral element method,
> where support points are used for quadrature also.
>
> Now I have to figure out some other way to do this efficiently. I want to
> avoid use of get_function_values.
>
> Best
> praveen
>
> On Wed, Nov 23, 2016 at 3:27 PM, luca.heltai <[email protected]> wrote:
> Not necessarily. In fact the ordering is reshuffled so that vertex support
> points comes first, then edge support points (3D), face support points, and
> lastly cell support points.
>
> To see the actual ordering, take a look at
>
> fe.get_unit_support_points()
>
> https://www.dealii.org/8.4.1/doxygen/deal.II/classFiniteElement.html#aa0169a82a73318973ad38e5785acdb27
>
> If you want to use this as a quadrature, you have to make sure that the
> weights are in the right order.
>
> L.
>
>
> > On 23 Nov 2016, at 10:26, Praveen C <[email protected]> wrote:
> >
> > Dear all
> >
> > Suppose I have
> >
> > FE_Q<dim> fe(degree);
> > QGaussLobatto<dim> quad(degree+1);
> >
> > Within a cell, I get
> >
> > FEValues<dim> fe_values(quad, update_quadrature_points);
> >
> > fe_values.reinit(cell);
> > cell->get_dof_indices(local_dof_indices);
> >
> > Then can I assume that, in the current cell,
> >
> > solution(local_dof_indices[q]) is the solution at
> > fe_values.quadrature_point(q) ?
> >
> > This is the case with DG spaces and I use this all the time. But I am not
> > sure about FE_Q.
> >
> > Thanks
> > praveen
> >
> > --
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