From: Martin Kronbichler <kronbichler@lnm.mw.tum.de>
Date: Sat, 9 Feb 2019 17:48:16 +0000 (+0100)
Subject: Add a comment about iteration 0.
X-Git-Tag: v9.1.0-rc1~338^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F7703%2Fhead;p=dealii.git

Add a comment about iteration 0.
---

diff --git a/include/deal.II/lac/precondition.h b/include/deal.II/lac/precondition.h
index 7d21d2cc0c..900c474fc7 100644
--- a/include/deal.II/lac/precondition.h
+++ b/include/deal.II/lac/precondition.h
@@ -1950,12 +1950,17 @@ namespace internal
       VectorUpdatesRange<Number>(upd, rhs.size());
 
       // swap vectors x^{n+1}->x^{n}, given the updates in the function above
-      if (iteration_index == 1)
+      if (iteration_index == 0)
+        {
+          // nothing to do here because we can immediately write into the
+          // solution vector without remembering any of the other vectors
+        }
+      else if (iteration_index == 1)
         {
           solution.swap(temp_vector1);
           solution_old.swap(temp_vector1);
         }
-      else if (iteration_index > 1)
+      else
         solution.swap(solution_old);
     }
 
@@ -1985,12 +1990,17 @@ namespace internal
       VectorUpdatesRange<Number>(upd, rhs.local_size());
 
       // swap vectors x^{n+1}->x^{n}, given the updates in the function above
-      if (iteration_index == 1)
+      if (iteration_index == 0)
+        {
+          // nothing to do here because we can immediately write into the
+          // solution vector without remembering any of the other vectors
+        }
+      else if (iteration_index == 1)
         {
           solution.swap(temp_vector1);
           solution_old.swap(temp_vector1);
         }
-      else if (iteration_index > 1)
+      else
         solution.swap(solution_old);
     }