From ea79fa079f6a71daac16a8d8f426c05564d4201b Mon Sep 17 00:00:00 2001
From: aprilnovak <novak@berkeley.edu>
Date: Wed, 18 Aug 2021 15:49:58 -0500
Subject: [PATCH] Allow constant scaling factor to be applied to libMesh
 unstructured meshes. Refs #1872

---
 include/openmc/mesh.h |  7 ++++++-
 src/mesh.cpp          | 25 ++++++++++++++++++++++++-
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/include/openmc/mesh.h b/include/openmc/mesh.h
index d3ca900cf5..7a55b5f206 100644
--- a/include/openmc/mesh.h
+++ b/include/openmc/mesh.h
@@ -492,7 +492,7 @@ class LibMesh : public UnstructuredMesh {
 public:
   // Constructors
   LibMesh(pugi::xml_node node);
-  LibMesh(const std::string& filename);
+  LibMesh(const std::string& filename, const double length_multiplier = 1.0);
 
   // Overridden Methods
   void bins_crossed(Position r0, Position r1, const Direction& u,
@@ -533,6 +533,9 @@ private:
   //! Translate an element pointer to a bin index
   int get_bin_from_element(const libMesh::Elem* elem) const;
 
+  //! Set the length multiplier to apply to each point in the mesh
+  void set_length_multiplier(const double length_multiplier);
+
   // Data members
   unique_ptr<libMesh::Mesh> m_; //!< pointer to the libMesh mesh instance
   vector<unique_ptr<libMesh::PointLocatorBase>>
@@ -547,6 +550,8 @@ private:
   libMesh::BoundingBox bbox_; //!< bounding box of the mesh
   libMesh::dof_id_type
     first_element_id_; //!< id of the first element in the mesh
+  double length_multiplier_ {1.0}; //!< Constant multiplication factor to apply to mesh coordinates
+  bool specified_length_multiplier_ {false};
 };
 
 #endif
diff --git a/src/mesh.cpp b/src/mesh.cpp
index 4798bfcf56..7770dfb865 100644
--- a/src/mesh.cpp
+++ b/src/mesh.cpp
@@ -35,6 +35,7 @@
 #ifdef LIBMESH
 #include "libmesh/mesh_tools.h"
 #include "libmesh/numeric_vector.h"
+#include "libmesh/mesh_modification.h"
 #endif
 
 namespace openmc {
@@ -2141,15 +2142,32 @@ void MOABMesh::write(const std::string& base_filename) const
 
 LibMesh::LibMesh(pugi::xml_node node) : UnstructuredMesh(node)
 {
+  // check if a length unit multiplier was specified
+  if (check_for_node(node, "length_multiplier")) {
+    length_multiplier_ = std::stod(get_node_value(node, "length_multiplier"));
+    specified_length_multiplier_ = true;
+  }
+
   initialize();
 }
 
-LibMesh::LibMesh(const std::string& filename)
+LibMesh::LibMesh(const std::string& filename, const double length_multiplier)
 {
   filename_ = filename;
+
+  if (length_multiplier != 1.0) {
+    set_length_multiplier(length_multiplier);
+  }
+
   initialize();
 }
 
+void LibMesh::set_length_multiplier(const double length_multiplier)
+{
+  length_multiplier_ = length_multiplier;
+  specified_length_multiplier_ = true;
+}
+
 void LibMesh::initialize()
 {
   if (!settings::libmesh_comm) {
@@ -2162,6 +2180,11 @@ void LibMesh::initialize()
 
   m_ = make_unique<libMesh::Mesh>(*settings::libmesh_comm, n_dimension_);
   m_->read(filename_);
+
+  if (specified_length_multiplier_) {
+    libMesh::MeshTools::Modification::scale(*m_, length_multiplier_);
+  }
+
   m_->prepare_for_use();
 
   // ensure that the loaded mesh is 3 dimensional