Thanks for the fast reply, this is exactly what I needed!
El miércoles, 22 de junio de 2016, 19:38:35 (UTC+2), bangerth escribió:
>
>
> > I am solving an eigenvalue problem similar than step-36. After solving
> for the
> > eigenpairs, I evaluate the eigenfunctions in the standard way:
> >
> > VectorTools::point_value ( mapping, dof_handler, efun[m],
> > q_points[j], Uq );
> >
> > where: efun[m] is the m-th eigenfunction from step-36,
> > q_points[j] are selected quadrature points,
> > Uq is where I store the FE evaluation.
> >
> > As expected, this operation is awfully slow! it takes seconds for a
> single
> > point evaluation with a decent discretization and having m
> eigenfunctions
> > makes it worse!
>
> Yes. But there is a much more efficient way to do this:
> FEValues fe_values (...);
> std::vector<double> sol_at_q_points (...);
> for (cell=...)
> {
> fe_values.reinit (cell);
> fe_values.get_function_values (efun[m], sol_at_q_points);
>
> This gives you the values of efun[m] at all quadrature points on the
> current
> cell at once, and this approach is efficient and independent of the
> overall
> size of the problem.
>
> Best
> W.
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth email: [email protected]
> <javascript:>
> www: http://www.math.tamu.edu/~bangerth/
>
>
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