From acfa8a551a46f780ab69ffa2e67cbada71a08e35 Mon Sep 17 00:00:00 2001
From: Jean-Paul Pelteret <jppelteret@gmail.com>
Date: Sat, 12 Aug 2017 01:05:43 -0600
Subject: [PATCH] Explicitly initialise tensor contraction results to zero.

---
 include/deal.II/base/tensor_accessors.h | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/include/deal.II/base/tensor_accessors.h b/include/deal.II/base/tensor_accessors.h
index 52c7ca7bf1..2ca2674e47 100644
--- a/include/deal.II/base/tensor_accessors.h
+++ b/include/deal.II/base/tensor_accessors.h
@@ -665,7 +665,9 @@ namespace TensorAccessors
       inline DEAL_II_ALWAYS_INLINE static
       T1 contract2(const T2 &left, const T3 &right)
       {
-        T1 result = T1();
+        // Some auto-differentiable numbers need explicit
+        // zero initialization.
+        T1 result = dealii::internal::NumberType<T1>::value(0.0);
         for (unsigned int i = 0; i < dim; ++i)
           result += Contract2<no_contr - 1, dim>::template contract2<T1>(left[i], right[i]);
         return result;
@@ -710,7 +712,9 @@ namespace TensorAccessors
       static inline
       T1 contract3(const T2 &left, const T3 &middle, const T4 &right)
       {
-        T1 result = T1();
+        // Some auto-differentiable numbers need explicit
+        // zero initialization.
+        T1 result = dealii::internal::NumberType<T1>::value(0.0);
         for (unsigned int i = 0; i < dim; ++i)
           result += Contract3<rank_1 - 1, rank_2, dim>::template contract3<T1>(left[i], middle[i], right);
         return result;
@@ -736,7 +740,9 @@ namespace TensorAccessors
       static inline
       T1 contract3(const T2 &left, const T3 &middle, const T4 &right)
       {
-        T1 result = T1();
+        // Some auto-differentiable numbers need explicit
+        // zero initialization.
+        T1 result = dealii::internal::NumberType<T1>::value(0.0);
         for (unsigned int i = 0; i < dim; ++i)
           result += Contract3<0, rank_2 - 1, dim>::template contract3<T1>(left, middle[i], right[i]);
         return result;
-- 
2.39.5