From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Wed, 12 Dec 2018 18:12:24 +0000 (-0700)
Subject: Ensure that DoFs not touched by VectorTools::interpolate don't get set.
X-Git-Tag: v9.1.0-rc1~475^2~2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=061d9ba0127dcdf87df160e8eaa696a91a3db555;p=dealii.git

Ensure that DoFs not touched by VectorTools::interpolate don't get set.
---

diff --git a/include/deal.II/numerics/vector_tools.templates.h b/include/deal.II/numerics/vector_tools.templates.h
index 6eac0117ad..b9f6b2f47c 100644
--- a/include/deal.II/numerics/vector_tools.templates.h
+++ b/include/deal.II/numerics/vector_tools.templates.h
@@ -515,14 +515,21 @@ namespace VectorTools
 
       for (const auto i : interpolation.locally_owned_elements())
         {
-          const auto value =
-            ::dealii::internal::ElementAccess<VectorType>::get(interpolation,
-                                                               i);
           const auto weight =
             ::dealii::internal::ElementAccess<VectorType>::get(weights, i);
-          ::dealii::internal::ElementAccess<VectorType>::set(value / weight,
-                                                             i,
-                                                             vec);
+
+          // See if we touched this DoF at all. If so, set the average
+          // of the value we computed in the output vector. Otherwise,
+          // don't touch the value at all.
+          if (weight != number(0))
+            {
+              const auto value =
+                ::dealii::internal::ElementAccess<VectorType>::get(
+                  interpolation, i);
+              ::dealii::internal::ElementAccess<VectorType>::set(value / weight,
+                                                                 i,
+                                                                 vec);
+            }
         }
       vec.compress(VectorOperation::insert);
     }