From: bangerth <bangerth@0785d39b-7218-0410-832d-ea1e28bc413d>
Date: Tue, 14 Apr 2009 21:48:20 +0000 (+0000)
Subject: Say something on the singularity of the matrix.
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=43f9c3a88af29b7d4d1c768e280524b4d476d75d;p=dealii-svn.git

Say something on the singularity of the matrix.


git-svn-id: https://svn.dealii.org/trunk@18611 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 7b44991a3a..07509c97c9 100644
--- a/deal.II/examples/step-34/step-34.cc
+++ b/deal.II/examples/step-34/step-34.cc
@@ -880,18 +880,20 @@ void BEMProblem<dim>::assemble_system() {
 				 // reality it only produces an LU
 				 // decomposition) and then apply this inverse
 				 // to the right hand side to yield the
-				 // solution:
+				 // solution.
+				 //
+				 // As mentioned in the introduction,
+				 // the solution is only known up to a
+				 // constant potential. We solve this
+				 // issue by subtracting the mean
+				 // value of the vector from each
+				 // vector entry to normalize it.
 template <int dim>
 void BEMProblem<dim>::solve_system() {
     SparseDirectUMFPACK inverse_matrix;
     inverse_matrix.initialize (system_matrix);
     inverse_matrix.vmult (phi, system_rhs);
 
-//TODO: is this true? it seems to me that the BIE is definite...    
-    // Since we are solving a purely Neumann problem, the solution is
-    // only known up to a constant potential. We solve this issue by
-    // subtracting the mean value of the vector from each vector
-    // entry.
     phi.add(-phi.mean_value());
 }