From: Wolfgang Bangerth <bangerth@math.tamu.edu>
Date: Wed, 19 Aug 2009 14:57:17 +0000 (+0000)
Subject: Fix a bug in a formula.
X-Git-Tag: v8.0.0~7256
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2b09d758638a503d27cfe4713693ea4e656d7a75;p=dealii.git

Fix a bug in a formula.

git-svn-id: https://svn.dealii.org/trunk@19312 0785d39b-7218-0410-832d-ea1e28bc413d
---

diff --git a/deal.II/doc/news/changes.h b/deal.II/doc/news/changes.h
index e9e97e08a0..876a9c5cf4 100644
--- a/deal.II/doc/news/changes.h
+++ b/deal.II/doc/news/changes.h
@@ -82,6 +82,26 @@ inconvenience this causes.
 <h3>General</h3>
 
 <ol>
+   <li>
+   <p>
+   Fixed: @ref step_31 "step-31" had a bug in the computation of the
+   global scaling parameter in the function that evaluates the artificial
+   viscosity: we computed
+   $c(\mathbf{u},T) = 
+    c_R\ \|\mathbf{u}\|_{L^\infty(\Omega)} \ \mathrm{var}(T)
+    \frac{1}{|\mathrm{diam}(\Omega)|^{\alpha-2}}$
+   when it should have been
+   $c(\mathbf{u},T) = 
+    c_R\ \|\mathbf{u}\|_{L^\infty(\Omega)} \ \mathrm{var}(T)
+    \ |\mathrm{diam}(\Omega)|^{\alpha-2}$. This didn't matter much in this
+   program because $\mathrm{diam}(\Omega)=2^{1/\textrm{dim}}$ and so is close
+   to one. It would matter, however, if the domain had been different, as
+   it is, for example, in @ref step_32 "step-32".
+   <br>
+   (WB 2009/08/19)
+   </p>
+   </li>
+
    <li>
    <p>
    Changed: When using Trilinos wrapper objects in parallel through MPI, each
diff --git a/deal.II/examples/step-31/step-31.cc b/deal.II/examples/step-31/step-31.cc
index e33facb240..6125b21223 100644
--- a/deal.II/examples/step-31/step-31.cc
+++ b/deal.II/examples/step-31/step-31.cc
@@ -1023,7 +1023,7 @@ compute_viscosity (const std::vector<double>          &old_temperature,
       max_velocity = std::max (std::sqrt (u*u), max_velocity);
     }
   
-  const double global_scaling = global_u_infty * global_T_variation /
+  const double global_scaling = global_u_infty * global_T_variation *
 				std::pow(global_Omega_diameter, alpha - 2.);
 
   return (beta *