From a38c6bc99047a17afff89672169b1bb41e70feab Mon Sep 17 00:00:00 2001 From: Wolfgang Bangerth Date: Tue, 29 May 2012 13:57:35 +0000 Subject: [PATCH] Add a comment following a suggestion by Daniel Gerecht (thanks!). git-svn-id: https://svn.dealii.org/trunk@25554 0785d39b-7218-0410-832d-ea1e28bc413d --- deal.II/doc/doxygen/headers/constraints.h | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/deal.II/doc/doxygen/headers/constraints.h b/deal.II/doc/doxygen/headers/constraints.h index 1a96c8519d..3e29400978 100644 --- a/deal.II/doc/doxygen/headers/constraints.h +++ b/deal.II/doc/doxygen/headers/constraints.h @@ -100,13 +100,23 @@ * This scheme of first building a linear system and then eliminating * constrained degrees of freedom is inefficient, and a bottleneck if there * are many constraints and matrices are full, i.e. especially for 3d and/or - * higher order or hp finite elements. We therefore offer a second way of + * higher order or hp finite elements. Furthermore, it is impossible to + * implement for %parallel computations where a process may not have access + * to elements of the matrix. We therefore offer a second way of * building linear systems, using the * ConstraintMatrix::add_entries_local_to_global() and * ConstraintMatrix::distribute_local_to_global() functions discussed * below. The resulting linear systems are equivalent to those one gets after * calling the ConstraintMatrix::condense() functions. * + * @note While these two ways are equivalent, i.e., the solution of + * linear systems computed via either approach is the same, the linear + * systems themselves do not necessarily have the same matrix and right + * hand side vector entries. Specifically, the matrix diagonal and right hand + * side entries corresponding to constrained degrees of freedom may be different + * as a result of the way in which we compute them; they are, however, always + * chosen in such a way that the solution to the linear system is the same. + * * *

Condensing matrices and sparsity patterns

* -- 2.39.5