From 310d1837ae241ab8576e16626287d6f4683cf4a0 Mon Sep 17 00:00:00 2001 From: Wolfgang Bangerth Date: Mon, 11 Jan 2021 17:51:31 -0700 Subject: [PATCH] Also point to the difference between nodal and non-nodal elements. --- .../deal.II/numerics/vector_tools_boundary.h | 22 ++++++++++++------- 1 file changed, 14 insertions(+), 8 deletions(-) diff --git a/include/deal.II/numerics/vector_tools_boundary.h b/include/deal.II/numerics/vector_tools_boundary.h index 332cdc0aad..813a3740a8 100644 --- a/include/deal.II/numerics/vector_tools_boundary.h +++ b/include/deal.II/numerics/vector_tools_boundary.h @@ -131,7 +131,9 @@ namespace VectorTools * that computing the projection is far more expensive than computing * the interpolation because the latter can be done one face at a time * whereas the projection requires the solution of a problem on the entire - * boundary. + * boundary. On the other hand, interpolation is only possible for + * "nodal" finite element spaces (such as FE_Q, but not + * FE_Q_Hierarchical), whereas the projection is always possible. */ template void @@ -415,13 +417,17 @@ namespace VectorTools * component number in @p boundary_functions that should be used for this * component in @p dof. By default, no remapping is applied. * - * @note Using the *projection* rather than the *interpolation* of boundary - * values makes relatively little difference in practice. That said, - * it is far more computationally expensive to compute projections because - * the require the solution of a problem that couples all unknowns on the - * boundary, whereas interpolation works on one face at a time. For - * some more theoretical considerations, see the documentation of the first - * interpolate_boundary_values() function above. + * @note Using the *projection* rather than the *interpolation* of + * boundary values makes relatively little difference in + * practice. That said, it is far more computationally expensive + * to compute projections because the require the solution of a + * problem that couples all unknowns on the boundary, whereas + * interpolation works on one face at a time. On the other hand, + * interpolation is only possible for "nodal" finite element + * spaces (such as FE_Q, but not FE_Q_Hierarchical), whereas the + * projection is always possible. (For some more theoretical + * considerations, see the documentation of the first + * interpolate_boundary_values() function above.) */ template void -- 2.39.5