Document the new compute_forcing_vector function.

git-svn-id: https://svn.dealii.org/trunk@16138 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/examples/step-33/step-33.cc b/deal.II/examples/step-33/step-33.cc
index 44da0a71fdcb742686f0f18881eed41faae10694..d539a1232db853d169b6ee96f35695d627330e64 100644 (file)
--- a/deal.II/examples/step-33/step-33.cc
+++ b/deal.II/examples/step-33/step-33.cc
@@ -370,6 +370,22 @@ struct EulerEquations
       }
 
 
+                                    // In the same way as describing the flux
+                                    // function $\mathbf F(\mathbf w), we
+                                    // also need to have a way to describe
+                                    // the right hand side forcing term. As
+                                    // mentioned in the introduction, we
+                                    // consider only gravity here, which
+                                    // leads to the specific form $\mathbf
+                                    // G(\mathbf w) = \left( \begin{array}{c}
+                                    // g_1\rho \\ g_2\rho \\ g_3\rho \\ 0
+                                    // \\ \rho \mathbf g \cdot \mathbf v
+                                    // \end{array} \right)$, shown here for
+                                    // the 3d case. More specifically, we
+                                    // will consider only $\mathbf
+                                    // g=(0,0,-1)^T$ in 3d, or $\mathbf
+                                    // g=(0,-1)^T$ in 2d. This naturally
+                                    // leads to the following function:
     template <typename InputVector, typename number>
     static
     void compute_forcing_vector (const InputVector &W,