Add important comment.

git-svn-id: https://svn.dealii.org/trunk@9262 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/deal.II/include/dofs/dof_handler.h b/deal.II/deal.II/include/dofs/dof_handler.h
index 44ae5b907d35f607a84abf96f5a09ecda478f738..6a87bc382fd4544254ce6a64de83b84fe3a55b84 100644 (file)
--- a/deal.II/deal.II/include/dofs/dof_handler.h
+++ b/deal.II/deal.II/include/dofs/dof_handler.h
@@ -372,6 +372,32 @@ class DoFHandler  :  public Subscriptor,
                                      * picture drawing. An example can be
                                      * found in the implementation of this
                                      * function.
+                                     *
+                                     * Note that this function is
+                                     * most often used to determine
+                                     * the maximal row length for
+                                     * sparsity
+                                     * patterns. Unfortunately, the
+                                     * while the estimates returned
+                                     * by this function are rather
+                                     * accurate in 1d and 2d, they
+                                     * are often significantly too
+                                     * high in 3d, leading the
+                                     * SparsityPattern class to
+                                     * allocate much too much memory
+                                     * in some cases. Unless someone
+                                     * comes around to improving the
+                                     * present function for 3d, there
+                                     * is not very much one can do
+                                     * about these cases. The typical
+                                     * way to work around this
+                                     * problem is to use an
+                                     * intermediate compressed
+                                     * sparsity pattern that only
+                                     * allocated memory on
+                                     * demand. Refer to the step-11
+                                     * example program on how to do
+                                     * this.
                                      */
     unsigned int max_couplings_between_dofs () const;