Improve docs.

git-svn-id: https://svn.dealii.org/trunk@4863 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/deal.II/include/dofs/dof_constraints.h b/deal.II/deal.II/include/dofs/dof_constraints.h
index 6b78a0466070653afeb1a19ec03a6570e7631070..cd293b1a04445eabca06ad142d6872a39e6d3e6b 100644 (file)
--- a/deal.II/deal.II/include/dofs/dof_constraints.h
+++ b/deal.II/deal.II/include/dofs/dof_constraints.h
@@ -116,18 +116,33 @@ class ConstraintMatrix : public Subscriptor
 
 
                                     /**
-                                     * Add a new line to the matrix.
+                                     * Add a new line to the
+                                     * matrix. If the line already
+                                     * exists, then the function
+                                     * simply returns.
                                      */
     void add_line (const unsigned int line);
 
                                     /**
-                                     * Add an entry to a given line. The list
-                                     * of lines is searched from the back to
-                                     * the front, so clever programming would
-                                     * add a new line (which is pushed to the
-                                     * back) and immediately afterwards fill
-                                     * the entries of that line. This way, no
-                                     * expensive searching is needed.
+                                     * Add an entry to a given
+                                     * line. The list of lines is
+                                     * searched from the back to the
+                                     * front, so clever programming
+                                     * would add a new line (which is
+                                     * pushed to the back) and
+                                     * immediately afterwards fill
+                                     * the entries of that line. This
+                                     * way, no expensive searching is
+                                     * needed.
+                                     *
+                                     * If an entry with the same
+                                     * indices as the one this
+                                     * function call denotes already
+                                     * exists, then this function
+                                     * simply returns provided that
+                                     * the value of the entry is the
+                                     * same. Thus, it does no harm to
+                                     * enter a constraint twice.
                                      */
     void add_entry (const unsigned int line,
                    const unsigned int column,