From 65be9996557c30c0f789eccf299e717eb80aac78 Mon Sep 17 00:00:00 2001
From: Daniel Arndt <arndtd@ornl.gov>
Date: Fri, 23 Aug 2019 19:15:05 +0000
Subject: [PATCH] Add initializing constructor to DiagonalMatrix

---
 doc/news/changes/minor/20190823DanielArndt |  4 ++++
 include/deal.II/lac/diagonal_matrix.h      | 15 ++++++++++++++-
 tests/lac/diagonal_matrix_02.cc            | 10 ++++------
 3 files changed, 22 insertions(+), 7 deletions(-)
 create mode 100644 doc/news/changes/minor/20190823DanielArndt

diff --git a/doc/news/changes/minor/20190823DanielArndt b/doc/news/changes/minor/20190823DanielArndt
new file mode 100644
index 0000000000..05ac2464bd
--- /dev/null
+++ b/doc/news/changes/minor/20190823DanielArndt
@@ -0,0 +1,4 @@
+New: There is a new constructor for DiagonalMatrix that immediately initializes
+the underlying vector.
+<br>
+(Daniel Arndt, 2019/08/23)
diff --git a/include/deal.II/lac/diagonal_matrix.h b/include/deal.II/lac/diagonal_matrix.h
index 48f87eef7b..86d96250db 100644
--- a/include/deal.II/lac/diagonal_matrix.h
+++ b/include/deal.II/lac/diagonal_matrix.h
@@ -52,10 +52,16 @@ public:
   using size_type  = typename VectorType::size_type;
 
   /**
-   * Constructor.
+   * Default constructor. The object needs still to be reinitialized to be
+   * usable.
    */
   DiagonalMatrix() = default;
 
+  /**
+   * Constructor immediately initializing the object properly.
+   */
+  explicit DiagonalMatrix(const VectorType &vec);
+
   /**
    * Initialize with a given vector by copying the content of the vector
    * @p vec.
@@ -215,6 +221,13 @@ private:
 
 #ifndef DOXYGEN
 
+template <typename VectorType>
+DiagonalMatrix<VectorType>::DiagonalMatrix(const VectorType &vec)
+  : diagonal(vec)
+{}
+
+
+
 template <typename VectorType>
 void
 DiagonalMatrix<VectorType>::clear()
diff --git a/tests/lac/diagonal_matrix_02.cc b/tests/lac/diagonal_matrix_02.cc
index e34af9249b..e48b7ce0bd 100644
--- a/tests/lac/diagonal_matrix_02.cc
+++ b/tests/lac/diagonal_matrix_02.cc
@@ -100,12 +100,10 @@ test(const bool hanging_nodes = true)
     sparse_matrix.reinit(csp);
   }
 
-  DiagonalMatrix<LinearAlgebra::distributed::Vector<double>> diagonal_matrix;
-  {
-    LinearAlgebra::distributed::Vector<double> dummy;
-    dummy.reinit(owned_set, relevant_set, MPI_COMM_WORLD);
-    diagonal_matrix.reinit(dummy);
-  }
+  DiagonalMatrix<LinearAlgebra::distributed::Vector<double>> diagonal_matrix(
+    LinearAlgebra::distributed::Vector<double>(owned_set,
+                                               relevant_set,
+                                               MPI_COMM_WORLD));
 
   {
     QGauss<dim> quadrature_formula(fe_degree + 1);
-- 
2.39.5