Add to documentation.

git-svn-id: https://svn.dealii.org/trunk@32610 0785d39b-7218-0410-832d-ea1e28bc413d

diff --git a/deal.II/include/deal.II/lac/trilinos_vector_base.h b/deal.II/include/deal.II/lac/trilinos_vector_base.h
index 2a933195271a3245c1f0da4d92733f9c3215ba0e..dfb77a229e69c80e2b1256133cdd9cfe8e248e27 100644 (file)
--- a/deal.II/include/deal.II/lac/trilinos_vector_base.h
+++ b/deal.II/include/deal.II/lac/trilinos_vector_base.h
@@ -674,7 +674,12 @@ namespace TrilinosWrappers
      * Simple vector addition, equal to the <tt>operator +=</tt>.
      *
      * Though, if the second argument <tt>allow_different_maps</tt> is set,
-     * then it is possible to add data from a different map.
+     * then it is possible to add data from a vector that uses a different
+     * map, i.e., a vector whose elements are split across processors
+     * differently. This may include vectors with ghost elements, for example.
+     * In general, however, adding vectors with a different element-to-processor
+     * map requires communicating data among processors and, consequently,
+     * is a slower operation than when using vectors using the same map.
      */
     void add (const VectorBase &V,
               const bool        allow_different_maps = false);