From 2fa4958037bfcb6a4e84c4923fa7786cc086be73 Mon Sep 17 00:00:00 2001
From: Mathias Anselmann <mathias.anselmann@posteo.de>
Date: Wed, 9 Jun 2021 17:31:43 +0200
Subject: [PATCH] added small test to verify that sparsity pattern is equal
 with one that comes from manual condensing

---
 .../flux_sparsity_pattern_constraints.cc      | 118 ++++++++++++++++++
 .../flux_sparsity_pattern_constraints.output  |   7 ++
 2 files changed, 125 insertions(+)
 create mode 100644 tests/multigrid/flux_sparsity_pattern_constraints.cc
 create mode 100644 tests/multigrid/flux_sparsity_pattern_constraints.output

diff --git a/tests/multigrid/flux_sparsity_pattern_constraints.cc b/tests/multigrid/flux_sparsity_pattern_constraints.cc
new file mode 100644
index 0000000000..79d58a124a
--- /dev/null
+++ b/tests/multigrid/flux_sparsity_pattern_constraints.cc
@@ -0,0 +1,118 @@
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2000 - 2021 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 generating a mg flux sparsity pattern without constraints and
+// later calling constraints.condense() on it results in the same pattern as
+// when creating the condensed pattern right away
+
+#include <deal.II/base/mg_level_object.h>
+
+#include <deal.II/dofs/dof_handler.h>
+#include <deal.II/dofs/dof_tools.h>
+
+#include <deal.II/fe/fe_q.h>
+#include <deal.II/fe/fe_system.h>
+
+#include <deal.II/grid/grid_generator.h>
+#include <deal.II/grid/tria.h>
+#include <deal.II/grid/tria_accessor.h>
+#include <deal.II/grid/tria_iterator.h>
+
+#include <deal.II/lac/affine_constraints.h>
+#include <deal.II/lac/dynamic_sparsity_pattern.h>
+#include <deal.II/lac/sparsity_pattern.h>
+
+#include <deal.II/multigrid/mg_constrained_dofs.h>
+
+#include "../tests.h"
+
+
+
+template <int dim>
+void
+check()
+{
+  constexpr unsigned int min_level{0}, max_level{2};
+
+  Triangulation<dim> tr(Triangulation<dim>::limit_level_difference_at_vertices);
+  GridGenerator::hyper_cube(tr);
+  tr.refine_global(max_level);
+
+  // create a system element composed
+  // of one Q1 and one Q2 element
+  FESystem<dim>   element(FE_Q<dim>(1), 1, FE_Q<dim>(2), 1);
+  DoFHandler<dim> dof(tr);
+  dof.distribute_dofs(element);
+  dof.distribute_mg_dofs();
+
+  MGLevelObject<AffineConstraints<double>> mg_constraints(min_level, max_level);
+
+  MGConstrainedDoFs mg_constrained_dofs;
+  mg_constrained_dofs.initialize(dof);
+
+  std::set<types::boundary_id> set_dirichlet;
+  set_dirichlet.insert(0);
+  mg_constrained_dofs.make_zero_boundary_constraints(dof, set_dirichlet);
+
+  // test sparsity patterns on each MG level
+  for (unsigned int l = min_level; l < max_level; ++l)
+    {
+      mg_constraints[l].reinit(dof.locally_owned_mg_dofs(l));
+      mg_constraints[l].add_lines(
+        mg_constrained_dofs.get_refinement_edge_indices(l));
+      mg_constraints[l].add_lines(mg_constrained_dofs.get_boundary_indices(l));
+      mg_constraints[l].close();
+
+      //--------------- Regular sparsity pattern checks -----------------
+      // first way: directly
+      SparsityPattern sparsity_1(dof.n_dofs(l), dof.n_dofs(l));
+      MGTools::make_flux_sparsity_pattern(dof, sparsity_1, l);
+      mg_constraints[l].condense(sparsity_1);
+      sparsity_1.compress();
+
+      // second way: via direct elimination of
+      // constraints
+      SparsityPattern        sparsity_2;
+      DynamicSparsityPattern dsp_2(dof.locally_owned_mg_dofs(l));
+      MGTools::make_flux_sparsity_pattern(dof, dsp_2, l, mg_constraints[l]);
+      sparsity_2.copy_from(dsp_2);
+
+      // tests if sparsity_[12] are equal
+      deallog << "Check 1:"
+              << " -- " << (sparsity_1 == sparsity_2 ? "ok" : "failed")
+              << std::endl;
+    }
+}
+
+
+
+int
+main()
+{
+  initlog();
+  deallog << std::setprecision(2) << std::fixed;
+
+  deallog.push("1d");
+  check<1>();
+  deallog.pop();
+  deallog.push("2d");
+  check<2>();
+  deallog.pop();
+  deallog.push("3d");
+  check<3>();
+  deallog.pop();
+}
diff --git a/tests/multigrid/flux_sparsity_pattern_constraints.output b/tests/multigrid/flux_sparsity_pattern_constraints.output
new file mode 100644
index 0000000000..362c8c9dc0
--- /dev/null
+++ b/tests/multigrid/flux_sparsity_pattern_constraints.output
@@ -0,0 +1,7 @@
+
+DEAL:1d::Check 1: -- ok
+DEAL:1d::Check 1: -- ok
+DEAL:2d::Check 1: -- ok
+DEAL:2d::Check 1: -- ok
+DEAL:3d::Check 1: -- ok
+DEAL:3d::Check 1: -- ok
-- 
2.39.5