From 909e47fdbe3c3d04a027eb580b8e6bf8c2688b67 Mon Sep 17 00:00:00 2001
From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Tue, 27 Aug 2024 17:48:32 -0600
Subject: [PATCH] Add a test.

---
 ...straints_make_consistent_in_parallel_04.cc | 89 +++++++++++++++++++
 ..._consistent_in_parallel_04.mpirun=2.output | 22 +++++
 2 files changed, 111 insertions(+)
 create mode 100644 tests/lac/constraints_make_consistent_in_parallel_04.cc
 create mode 100644 tests/lac/constraints_make_consistent_in_parallel_04.mpirun=2.output

diff --git a/tests/lac/constraints_make_consistent_in_parallel_04.cc b/tests/lac/constraints_make_consistent_in_parallel_04.cc
new file mode 100644
index 0000000000..92efe5f25e
--- /dev/null
+++ b/tests/lac/constraints_make_consistent_in_parallel_04.cc
@@ -0,0 +1,89 @@
+// ------------------------------------------------------------------------
+//
+// SPDX-License-Identifier: LGPL-2.1-or-later
+// Copyright (C) 2018 - 2023 by the deal.II authors
+//
+// This file is part of the deal.II library.
+//
+// Part of the source code is dual licensed under Apache-2.0 WITH
+// LLVM-exception OR LGPL-2.1-or-later. Detailed license information
+// governing the source code and code contributions can be found in
+// LICENSE.md and CONTRIBUTING.md at the top level directory of deal.II.
+//
+// ------------------------------------------------------------------------
+
+
+
+// test AffineConstraints<double>::make_consistent_in_parallel for case
+// where constraints need to be combined between different ranks
+
+#include <deal.II/base/index_set.h>
+
+#include <deal.II/lac/affine_constraints.h>
+
+#include "../tests.h"
+
+using namespace dealii;
+
+void
+test()
+{
+  IndexSet locally_owned_dofs(3);
+  if (Utilities::MPI::this_mpi_process(MPI_COMM_WORLD) == 0)
+    locally_owned_dofs.add_range(0, 2);
+  else if (Utilities::MPI::this_mpi_process(MPI_COMM_WORLD) == 1)
+    locally_owned_dofs.add_range(2, 3);
+
+  IndexSet                  locally_relevant_dofs = complete_index_set(3);
+  AffineConstraints<double> constraints(locally_owned_dofs,
+                                        locally_relevant_dofs);
+
+  const auto show_constraints_1_2 = [&]() {
+    deallog << "What process "
+            << Utilities::MPI::this_mpi_process(MPI_COMM_WORLD)
+            << " believes about DoF 1:" << std::endl;
+    for (const auto &c : constraints.get_lines())
+      if (c.index == 1)
+        for (const auto &entry : c.entries)
+          deallog << "    constrained against " << entry.first
+                  << " with weight " << entry.second << std::endl;
+    deallog << "What process "
+            << Utilities::MPI::this_mpi_process(MPI_COMM_WORLD)
+            << " believes about DoF 2:" << std::endl;
+    for (const auto &c : constraints.get_lines())
+      if (c.index == 2)
+        for (const auto &entry : c.entries)
+          deallog << "    constrained against " << entry.first
+                  << " with weight " << entry.second << std::endl;
+  };
+
+
+  deallog << "------------- make_hanging_node_constraints():" << std::endl;
+  if (Utilities::MPI::this_mpi_process(MPI_COMM_WORLD) == 0)
+    {
+      constraints.add_constraint(1, {{0, 0.5}});
+      constraints.add_constraint(2, {{0, 0.25}});
+    }
+  else if (Utilities::MPI::this_mpi_process(MPI_COMM_WORLD) == 1)
+    {
+      constraints.add_constraint(2, {{1, 0.5}});
+    }
+  show_constraints_1_2();
+
+  deallog << "------------- make_consistent_in_parallel():" << std::endl;
+  constraints.make_consistent_in_parallel(locally_owned_dofs,
+                                          locally_relevant_dofs,
+                                          MPI_COMM_WORLD);
+  show_constraints_1_2();
+}
+
+
+
+int
+main(int argc, char *argv[])
+{
+  Utilities::MPI::MPI_InitFinalize mpi_init(argc, argv);
+  MPILogInitAll                    all;
+
+  test();
+}
diff --git a/tests/lac/constraints_make_consistent_in_parallel_04.mpirun=2.output b/tests/lac/constraints_make_consistent_in_parallel_04.mpirun=2.output
new file mode 100644
index 0000000000..5cf9f89b78
--- /dev/null
+++ b/tests/lac/constraints_make_consistent_in_parallel_04.mpirun=2.output
@@ -0,0 +1,22 @@
+
+DEAL:0::------------- make_hanging_node_constraints():
+DEAL:0::What process 0 believes about DoF 1:
+DEAL:0::    constrained against 0 with weight 0.500000
+DEAL:0::What process 0 believes about DoF 2:
+DEAL:0::    constrained against 0 with weight 0.250000
+DEAL:0::------------- make_consistent_in_parallel():
+DEAL:0::What process 0 believes about DoF 1:
+DEAL:0::    constrained against 0 with weight 0.500000
+DEAL:0::What process 0 believes about DoF 2:
+DEAL:0::    constrained against 0 with weight 0.250000
+
+DEAL:1::------------- make_hanging_node_constraints():
+DEAL:1::What process 1 believes about DoF 1:
+DEAL:1::What process 1 believes about DoF 2:
+DEAL:1::    constrained against 1 with weight 0.500000
+DEAL:1::------------- make_consistent_in_parallel():
+DEAL:1::What process 1 believes about DoF 1:
+DEAL:1::    constrained against 0 with weight 0.500000
+DEAL:1::What process 1 believes about DoF 2:
+DEAL:1::    constrained against 0 with weight 0.250000
+
-- 
2.39.5