Add a paragraph.

git-svn-id: https://svn.dealii.org/trunk@8981 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/doc/tutorial/chapter-2.step-by-step/step-17.data/intro.html b/deal.II/doc/tutorial/chapter-2.step-by-step/step-17.data/intro.html
index 5a921a0a88ba825a467d88686988d2ef43f6ef60..f524fcc3e032db102aab52b9ec07dd48be0ecee8 100644 (file)
--- a/deal.II/doc/tutorial/chapter-2.step-by-step/step-17.data/intro.html
+++ b/deal.II/doc/tutorial/chapter-2.step-by-step/step-17.data/intro.html
@@ -51,6 +51,19 @@ time, PETSc provides dummy MPI stubs that allow to run the same program on a
 single machine if so desired, without any changes.
 </p>
 
+<p>
+Note, however, that the only data structures we parallelize are matrices and
+vectors. We do, in particular, not split up the <code>Triangulation</code> and
+<code>DoFHandler</code> classes: each process still has a complete copy of
+these objects, and all processes have exact copies of what the other processes
+have. Parallelizing the data structures used in hierarchic and unstructured
+triangulations is a very hard problem, and we do not attempt to do so at
+present. It also requires that many more aspects of the application program
+have to be changed, since for example loops over all cells can only include
+locally available cells. We thus went for the path of least resistance and
+only parallelized the linear algebra part.
+</p>
+
 <p>
 The techniques this program demonstrates are: how to use the PETSc wrapper
 classes; how to parallelize operations for jobs running on an MPI network; and