Augment docs.

git-svn-id: https://svn.dealii.org/trunk@18703 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/examples/step-34/step-34.cc b/deal.II/examples/step-34/step-34.cc
index 47e842205fec6d61fc69ca9142b1cae6f5d21196..5a81e76a485cbb0b28a783681d1fc4006e57b2e8 100644 (file)
--- a/deal.II/examples/step-34/step-34.cc
+++ b/deal.II/examples/step-34/step-34.cc
@@ -1320,24 +1320,31 @@ void BEMProblem<dim>::assemble_system()
                                 // the linear system.
                                 //
                                 // As mentioned in the introduction,
-                                // the fact that the system matrix
-                                // has a non null kernel, requires us
-                                // to be careful in case we wish to
-                                // use an iterative solver. To
+                                // the system matrix is singular with
+                                // a kernel that contains the
+                                // constant functions. This requires
+                                // us to be careful in case we wish
+                                // to use an iterative solver. To
                                 // address this issue, we use two new
                                 // instruments of the library: the
                                 // MeanValueFilter class, and the
                                 // ProductMatrix class. The
-                                // MeanValueFilter has the same
-                                // interface of a matrix, with the
-                                // effect of subtracting the mean
-                                // value to source vector. We cascade
+                                // MeanValueFilter has the interface
+                                // of a matrix (i.e. it has a
+                                // function MeanValueFilter::vmult),
+                                // with the effect that the output
+                                // vector equals the input vector
+                                // minus its mean value. We cascade
                                 // this operator with the system
                                 // matrix, and we obtain a matrix
                                 // whose result is renormalized to a
-                                // zero mean value Vector. This
-                                // object is then passed to a GMRES
-                                // solver.
+                                // zero mean value Vector. In other
+                                // words, vectors that are multiplied
+                                // have mean value zero and therefore
+                                // never feel the fact that the
+                                // system matrix has a kernel for
+                                // these. The combined matrix object
+                                // is then passed to a GMRES solver.
 template <int dim>
 void BEMProblem<dim>::solve_system()
 {