extend glossary about compress()

git-svn-id: https://svn.dealii.org/trunk@28559 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/doc/doxygen/headers/glossary.h b/deal.II/doc/doxygen/headers/glossary.h
index 2c100e538bee34ec7daa4e6f06c746d130dbb860..35f4ff9d202be07154df28e88a4db21a22df7f93 100644 (file)
--- a/deal.II/doc/doxygen/headers/glossary.h
+++ b/deal.II/doc/doxygen/headers/glossary.h
@@ -565,6 +565,22 @@
  * Some of the objects are also indifferent and can figure out what to
  * do without being told. The TrilinosWrappers::SparseMatrix can do that,
  * for example.
+ *
+ * In short, you need to call compress() in the following cases (and
+ * only in those cases, though calling compress() in other cases
+ * just costs some performance):
+ *
+ * 1. At the end of your assembly loop on matrices and vectors. This needs to
+ * be done if you write entries directly and if you use
+ * ConstraintMatrix::distribute_local_to_global. Use VectorOperation::add.
+ *
+ * 2. When you are done setting individual elements in a matrix/vector before
+ * any other operations are done (adding to elements, other operations like
+ * scaling, solving, reading, etc.). Use VectorOperation::insert.
+ *
+ * 3. Like in 2., but for adding values to individual elements. Use
+ * VectorOperation::add.
+ *
  * </dd>
  *
  *