From 7ca172d4461c771c3bc1db2f4317ced1b614a483 Mon Sep 17 00:00:00 2001
From: bangerth <bangerth@0785d39b-7218-0410-832d-ea1e28bc413d>
Date: Wed, 5 Mar 2014 00:31:34 +0000
Subject: [PATCH] Add to documentation.

git-svn-id: https://svn.dealii.org/trunk@32610 0785d39b-7218-0410-832d-ea1e28bc413d
---
 deal.II/include/deal.II/lac/trilinos_vector_base.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

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 2a93319527..dfb77a229e 100644
--- 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);
-- 
2.39.5