From 373d1e32082fc3f42da1363f300a666c07167e7c Mon Sep 17 00:00:00 2001 From: Wolfgang Bangerth Date: Mon, 15 Nov 2004 22:00:14 +0000 Subject: [PATCH] Add a comment. git-svn-id: https://svn.dealii.org/trunk@9761 0785d39b-7218-0410-832d-ea1e28bc413d --- deal.II/deal.II/include/grid/tria_accessor.h | 31 +++++++++++++++++++- 1 file changed, 30 insertions(+), 1 deletion(-) diff --git a/deal.II/deal.II/include/grid/tria_accessor.h b/deal.II/deal.II/include/grid/tria_accessor.h index 604d176acb..7e2632f3b1 100644 --- a/deal.II/deal.II/include/grid/tria_accessor.h +++ b/deal.II/deal.II/include/grid/tria_accessor.h @@ -2521,7 +2521,9 @@ class CellAccessor : public TriaObjectAccessor * asking * @p GeometryInfo::child_cell_on_subface * for the index of the - * child. However, the function + * child. + * + * However, the function * is more complicated in 3d, * since there faces may have * more than one orientation, and @@ -2530,6 +2532,33 @@ class CellAccessor : public TriaObjectAccessor * this and the neighbor cell to * figure out which cell we want * to have. + * + * This can lead to surprising results: + * if we are sitting on a cell and are + * asking for a cell behind subface @sf, + * then this means that we are + * considering the subface for the face + * in the natural direction for the + * present cell. However, if the face as + * seen from this cell has + * face_orientation()==false, + * then the child of the face that + * separates the present cell from the + * neighboring cell's child is not + * necessarily the @p sf-th child of the + * face of this cell. This is so because + * the @p subface_no parameter to this + * function corresponds to the subface + * with respect to the intrinsic ordering + * of the present cell, whereas children + * of face iterators are computed with + * respect to the intrinsic ordering of + * faces; these two orderings are only + * identical if the face orientation is + * @p true, and reversed otherwise. + * + * Fortunately, this is only very rarely + * of concern. */ TriaIterator > neighbor_child_on_subface (const unsigned int face_no, -- 2.39.5