From: bangerth <bangerth@0785d39b-7218-0410-832d-ea1e28bc413d>
Date: Thu, 21 Feb 2013 20:24:29 +0000 (+0000)
Subject: Note something in relation to step-20.
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2bdff4a8f23d0c82bab964220ea7a694996c5ae1;p=dealii-svn.git

Note something in relation to step-20.


git-svn-id: https://svn.dealii.org/trunk@28517 0785d39b-7218-0410-832d-ea1e28bc413d
---

diff --git a/deal.II/examples/step-21/doc/intro.dox b/deal.II/examples/step-21/doc/intro.dox
index d5f8782c55..85ce8f313a 100644
--- a/deal.II/examples/step-21/doc/intro.dox
+++ b/deal.II/examples/step-21/doc/intro.dox
@@ -324,7 +324,12 @@ M^S_{ij} &=&
 (S^n,\phi_i)_\Omega +\triangle t \sum_K  \left(F(S^n) q^{n+1}, \phi_i\right)_K.
 @f}
 
-Note the following complication, however: Since the matrix $H_{ij}$
+@note Due to historical accidents, the role of matrices $B$ and $B^T$
+has been reverted in this program compared to step-20. In other words,
+here $B$ refers to the divergence and $B^T$ to the gradient operators
+when it was the other way around in step-20.
+
+The system above presents a complication: Since the matrix $H_{ij}$
 depends on $\mathbf u^{n+1}$ implicitly (the velocities are needed to
 determine which parts of the boundaries $\partial K$ of cells are
 influx or outflux parts), we can only assemble this matrix after we