From 641cd83873e1578979371eb4b301f34e30d03df8 Mon Sep 17 00:00:00 2001
From: bangerth <bangerth@0785d39b-7218-0410-832d-ea1e28bc413d>
Date: Sun, 19 Dec 2010 20:24:14 +0000
Subject: [PATCH] Add to documentation.

git-svn-id: https://svn.dealii.org/trunk@23011 0785d39b-7218-0410-832d-ea1e28bc413d
---
 deal.II/include/deal.II/fe/mapping_q1.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/deal.II/include/deal.II/fe/mapping_q1.h b/deal.II/include/deal.II/fe/mapping_q1.h
index 245c90fe10..74e2871984 100644
--- a/deal.II/include/deal.II/fe/mapping_q1.h
+++ b/deal.II/include/deal.II/fe/mapping_q1.h
@@ -219,6 +219,21 @@ class MappingQ1 : public Mapping<dim,spacedim>
 					  * i.e. $J_{ij}=dx_i/d\hat x_j$.
 					  *
 					  * Computed on each cell.
+					  *
+					  * @note If dim<spacedim,
+					  * then the Jacobian matrix
+					  * is rectangular, with
+					  * spacedim rows and dim
+					  * columns. We nevertheless
+					  * store it as a square
+					  * rank-2 tensor. The unused
+					  * columns are internally
+					  * used to store temporary
+					  * data, such as the
+					  * "missing" vectors spanning
+					  * the full space (for
+					  * example the cell normal
+					  * vector).
 					  */
 	std::vector<Tensor<2,spacedim> > contravariant;
 
-- 
2.39.5