From: Timo Heister <timo.heister@gmail.com>
Date: Thu, 7 Aug 2014 15:40:13 +0000 (-0400)
Subject: improve patch slightly
X-Git-Tag: v8.2.0-rc1~208^2~1
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=44af8d44e5c893f0d043e580e71425dc7815f6a9;p=dealii.git

improve patch slightly
---

diff --git a/include/deal.II/lac/constraint_matrix.h b/include/deal.II/lac/constraint_matrix.h
index 282fa05f95..09edea34f7 100644
--- a/include/deal.II/lac/constraint_matrix.h
+++ b/include/deal.II/lac/constraint_matrix.h
@@ -649,22 +649,22 @@ public:
    * account and throws an exception in case there are any
    * inhomogeneities. Use the function using both a matrix and vector for that
    * case.
-   * Note: this function does not work for MPI vectors because it would require 
-   * ghosted vector in that case, however all ghosted vectors are read-only objects.
-   * Instead, use the analogue with two input arguments.
+   *
+   * @note This function does not work for MPI vectors. Use condense() with
+   * two vector arguments instead.
    */
   template <class VectorType>
   void condense (VectorType &vec) const;
 
   /**
-   * Same as above, but accepts two input arguments. If called in parallel, one 
-   * vector is supposed to be a ghosted vector and the other vector without ghost
-   * elements. The function copies and condenses values from @p vec_ghosted into 
-   * @p vec.
+   * The function copies and condenses values from @p vec_ghosted into @p
+   * output. In a serial code it is equivalent to calling condense (vec). If
+   * called in parallel, @p vec_ghosted is supposed to contain ghost elements
+   * while @p output should not.
    */
   template <class VectorType>
   void condense (const VectorType &vec_ghosted,
-                 VectorType       &vec) const;
+                 VectorType       &output) const;
 
   /**
    * Condense a given matrix and a given vector. The associated matrix struct
diff --git a/include/deal.II/lac/constraint_matrix.templates.h b/include/deal.II/lac/constraint_matrix.templates.h
index d54eca03e6..12136a8b70 100644
--- a/include/deal.II/lac/constraint_matrix.templates.h
+++ b/include/deal.II/lac/constraint_matrix.templates.h
@@ -78,7 +78,9 @@ ConstraintMatrix::condense (const VectorType &vec_ghosted,
 {
   Assert (sorted == true, ExcMatrixNotClosed());
 
-  vec = vec_ghosted;
+  // if this is called with different arguments, we need to copy the data over:
+  if (&vec != &vec_ghosted)
+    vec = vec_ghosted;
 
   // distribute all entries, and set them to zero. do so in
   // two loops because in the first one we need to add to elements