From e382a18fc19db0d87f0c7346c9aa5601815e25c2 Mon Sep 17 00:00:00 2001
From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Wed, 11 Jan 2023 12:06:27 -0700
Subject: [PATCH] Add a test.

---
 tests/grid/reference_cell_type_04.cc     | 93 ++++++++++++++++++++++++
 tests/grid/reference_cell_type_04.output | 22 ++++++
 2 files changed, 115 insertions(+)
 create mode 100644 tests/grid/reference_cell_type_04.cc
 create mode 100644 tests/grid/reference_cell_type_04.output

diff --git a/tests/grid/reference_cell_type_04.cc b/tests/grid/reference_cell_type_04.cc
new file mode 100644
index 0000000000..07e13e9ae8
--- /dev/null
+++ b/tests/grid/reference_cell_type_04.cc
@@ -0,0 +1,93 @@
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2020 - 2022 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.
+//
+// ---------------------------------------------------------------------
+
+
+// Test consistency of ReferenceCell::volume() and
+// ReferenceCell::contains_point() by computing a Monte Carlo integral
+// of the volume based on the characteristic function implied by
+// contains_point().
+
+#include <deal.II/grid/reference_cell.h>
+
+#include <random>
+
+#include "../tests.h"
+
+
+using namespace dealii;
+
+template <int dim>
+void
+test(const ReferenceCell &reference_cell)
+{
+  unsigned int       n_samples_inside = 0;
+  const unsigned int n_samples        = 200000;
+
+  std::uniform_real_distribution<> uniform_distribution(-1., 1.);
+  std::mt19937                     rng;
+
+  for (unsigned int n = 0; n < n_samples; ++n)
+    {
+      // Choose a random point in the box [-1,1]^d that contains all
+      // of our reference cells:
+      Point<dim> p;
+      for (unsigned int d = 0; d < dim; ++d)
+        p[d] = uniform_distribution(rng);
+
+      if (reference_cell.contains_point(p))
+        ++n_samples_inside;
+    }
+
+  // The approximate volume of the reference cell is then the fraction
+  // of points that were found to be within the reference cell times
+  // the volume of the box within which we have sampled:
+  const double volume = 1. * n_samples_inside / n_samples * std::pow(2.0, dim);
+
+  deallog << "ReferenceCell: " << reference_cell.to_string() << std::endl;
+  deallog << "  self-reported volume = " << reference_cell.volume()
+          << std::endl;
+  deallog << "  computed approximate volume = " << volume << std::endl;
+
+  Assert(std::fabs(volume - reference_cell.volume()) < 1e-2,
+         ExcInternalError());
+}
+
+int
+main()
+{
+  initlog();
+
+  {
+    deallog.push("1D");
+    test<1>(ReferenceCells::Line);
+    deallog.pop();
+  }
+
+  {
+    deallog.push("2D");
+    test<2>(ReferenceCells::Quadrilateral);
+    test<2>(ReferenceCells::Triangle);
+    deallog.pop();
+  }
+
+  {
+    deallog.push("3D");
+    test<3>(ReferenceCells::Tetrahedron);
+    test<3>(ReferenceCells::Pyramid);
+    test<3>(ReferenceCells::Wedge);
+    test<3>(ReferenceCells::Hexahedron);
+    deallog.pop();
+  }
+}
diff --git a/tests/grid/reference_cell_type_04.output b/tests/grid/reference_cell_type_04.output
new file mode 100644
index 0000000000..8eadf35e7d
--- /dev/null
+++ b/tests/grid/reference_cell_type_04.output
@@ -0,0 +1,22 @@
+
+DEAL:1D::ReferenceCell: Line
+DEAL:1D::  self-reported volume = 1.00000
+DEAL:1D::  computed approximate volume = 1.00091
+DEAL:2D::ReferenceCell: Quad
+DEAL:2D::  self-reported volume = 1.00000
+DEAL:2D::  computed approximate volume = 0.998800
+DEAL:2D::ReferenceCell: Tri
+DEAL:2D::  self-reported volume = 0.500000
+DEAL:2D::  computed approximate volume = 0.498940
+DEAL:3D::ReferenceCell: Tet
+DEAL:3D::  self-reported volume = 0.166667
+DEAL:3D::  computed approximate volume = 0.166560
+DEAL:3D::ReferenceCell: Pyramid
+DEAL:3D::  self-reported volume = 1.33333
+DEAL:3D::  computed approximate volume = 1.33892
+DEAL:3D::ReferenceCell: Wedge
+DEAL:3D::  self-reported volume = 0.500000
+DEAL:3D::  computed approximate volume = 0.496800
+DEAL:3D::ReferenceCell: Hex
+DEAL:3D::  self-reported volume = 1.00000
+DEAL:3D::  computed approximate volume = 0.994000
-- 
2.39.5