From: Wolfgang Bangerth Date: Tue, 14 Apr 2009 21:48:20 +0000 (+0000) Subject: Say something on the singularity of the matrix. X-Git-Tag: v8.0.0~7854 X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3fff0b31ac1b1eb23eeea17fba06d5a0f97019b8;p=dealii.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::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 void BEMProblem::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()); }