From 821228dc8f64a154659eb79d3d9b2197ebd028df Mon Sep 17 00:00:00 2001 From: bangerth Date: Thu, 23 Apr 2009 16:03:58 +0000 Subject: [PATCH] Augment docs. git-svn-id: https://svn.dealii.org/trunk@18703 0785d39b-7218-0410-832d-ea1e28bc413d --- deal.II/examples/step-34/step-34.cc | 29 ++++++++++++++++++----------- 1 file changed, 18 insertions(+), 11 deletions(-) diff --git a/deal.II/examples/step-34/step-34.cc b/deal.II/examples/step-34/step-34.cc index 47e842205f..5a81e76a48 100644 --- a/deal.II/examples/step-34/step-34.cc +++ b/deal.II/examples/step-34/step-34.cc @@ -1320,24 +1320,31 @@ void BEMProblem::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 void BEMProblem::solve_system() { -- 2.39.5