Add assertion to PETScWrappers::MatrixBase::begin() and end().

Add assertion to make sure that begin() and end() can only be called on a processor owning the entire matrix. Also make sure that begin() works in case the first row(s) of the matrix is(are) emtpy.
Fixes #8571.

diff --git a/doc/news/changes/minor/20190819SebastianStark b/doc/news/changes/minor/20190819SebastianStark
new file mode 100644 (file)
index 0000000..6372de1
--- /dev/null
+++ b/doc/news/changes/minor/20190819SebastianStark
@@ -0,0 +1,3 @@
+Fixed: Make sure that begin() and end() of PETScWrappers::MatrixBase can only be called on a processor owning all rows of the matrix. Also fix a bug which caused begin() to fail when the first row(s) of the matrix is(are) empty.
+<br>
+(Sebastian Stark, 2019/08/19)

diff --git a/include/deal.II/lac/petsc_matrix_base.h b/include/deal.II/lac/petsc_matrix_base.h
index 1b8bbc48e0c8a12070251eed8d6da3eaf1afc65d..2716196be4503d9c382208a2dbc7653fcfadd4cc 100644 (file)
--- a/include/deal.II/lac/petsc_matrix_base.h
+++ b/include/deal.II/lac/petsc_matrix_base.h
@@ -837,13 +837,17 @@ namespace PETScWrappers
     residual(VectorBase &dst, const VectorBase &x, const VectorBase &b) const;
 
     /**
-     * Iterator starting at the first entry.
+     * Iterator starting at the first entry. This can only be called on a
+     * processor owning the entire matrix. In all other cases refer to the
+     * version of begin() taking a row number as an argument.
      */
     const_iterator
     begin() const;
 
     /**
-     * Final iterator.
+     * Final iterator. This can only be called on a processor owning the entire
+     * matrix. In all other cases refer to the version of end() taking a row
+     * number as an argument.
      */
     const_iterator
     end() const;
@@ -1491,13 +1495,29 @@ namespace PETScWrappers
   inline MatrixBase::const_iterator
   MatrixBase::begin() const
   {
-    return const_iterator(this, 0, 0);
+    Assert(
+      (in_local_range(0) && in_local_range(m() - 1)),
+      ExcMessage(
+        "begin() and end() can only be called on a processor owning the entire matrix. If this is a distributed matrix, use begin(row) and end(row) instead."));
+
+    // find the first non-empty row in order to make sure that the returned
+    // iterator points to something useful
+    size_type first_nonempty_row = 0;
+    while ((first_nonempty_row < m()) && (row_length(first_nonempty_row) == 0))
+      ++first_nonempty_row;
+
+    return const_iterator(this, first_nonempty_row, 0);
   }
 
 
   inline MatrixBase::const_iterator
   MatrixBase::end() const
   {
+    Assert(
+      (in_local_range(0) && in_local_range(m() - 1)),
+      ExcMessage(
+        "begin() and end() can only be called on a processor owning the entire matrix. If this is a distributed matrix, use begin(row) and end(row) instead."));
+
     return const_iterator(this, m(), 0);
   }
 

diff --git a/tests/petsc/matrix_base_iterator_01.cc b/tests/petsc/matrix_base_iterator_01.cc
new file mode 100644 (file)
index 0000000..4bb63ae
--- /dev/null
+++ b/tests/petsc/matrix_base_iterator_01.cc
@@ -0,0 +1,53 @@
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2004 - 2018 by the deal.II authors
+//
+// This file is part of the deal.II library.
+//
+// The deal.II library is free software; you can use it, redistribute
+// it, and/or modify it under the terms of the GNU Lesser General
+// Public License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+// The full text of the license can be found in the file LICENSE.md at
+// the top level directory of deal.II.
+//
+// ---------------------------------------------------------------------
+
+
+
+// check that begin() works if the first row(s) is(are) empty
+
+#include <deal.II/lac/dynamic_sparsity_pattern.h>
+#include <deal.II/lac/petsc_sparse_matrix.h>
+
+#include "../tests.h"
+
+
+void
+test()
+{
+  // test the case that the first row is empty
+  dealii::DynamicSparsityPattern dsp_1(2);
+  dsp_1.add(1, 1);
+
+  PETScWrappers::SparseMatrix K_1(dsp_1);
+
+  if (K_1.begin()->row() == 1)
+    deallog << "OK" << std::endl;
+
+  // test the case that the entire matrix is empty
+  dealii::DynamicSparsityPattern dsp_2(2);
+
+  PETScWrappers::SparseMatrix K_2(dsp_2);
+
+  if (K_2.begin() == K_2.end())
+    deallog << "OK" << std::endl;
+}
+
+int
+main(int argc, char **argv)
+{
+  Utilities::MPI::MPI_InitFinalize mpi_initialization(argc, argv, 1);
+  initlog();
+  test();
+}

diff --git a/tests/petsc/matrix_base_iterator_01.output b/tests/petsc/matrix_base_iterator_01.output
new file mode 100644 (file)
index 0000000..8b3b075
--- /dev/null
+++ b/tests/petsc/matrix_base_iterator_01.output
@@ -0,0 +1,3 @@
+
+DEAL::OK
+DEAL::OK