Add length_multiplier to python API. Refs #1872

docs/source/io_formats/tallies.rst

@@ -318,6 +318,10 @@ attributes/sub-elements:
   :dimension:
     The number of mesh cells in each direction. (For regular mesh only.)
 
+  :length_multiplier:
+    A multiplicative factor to apply to the mesh coordinates in all directions.
+    (For unstructured mesh only.)
+
   :lower_left:
     The lower-left corner of the structured mesh. If only two coordinates are
     given, it is assumed that the mesh is an x-y mesh. (For regular mesh only.)

openmc/mesh.py

@@ -611,6 +611,8 @@ class UnstructuredMesh(MeshBase):
     ----------
     filename : str
         Location of the unstructured mesh file
+    length_multiplier: float
+        Constant multiplier to apply to mesh coordinates
     mesh_id : int
         Unique identifier for the mesh
     name : str
@@ -626,11 +628,16 @@ class UnstructuredMesh(MeshBase):
         Name of the mesh
     filename : str
         Name of the file containing the unstructured mesh
+    length_multiplier: float
+        Multiplicative factor to apply to mesh coordinates
     library : str
         Mesh library used for the unstructured mesh tally
     output : bool
         Indicates whether or not automatic tally output should
         be generated for this mesh
+    specified_length_multiplier: bool
+        Indicates whether a non-unity length multiplier has been
+        applied to this mesh
     volumes : Iterable of float
         Volumes of the unstructured mesh elements
     total_volume : float
@@ -639,13 +646,15 @@ class UnstructuredMesh(MeshBase):
         An iterable of element centroid coordinates, e.g. [(0.0, 0.0, 0.0),
         (1.0, 1.0, 1.0), ...]
     """
-    def __init__(self, filename, library, mesh_id=None, name=''):
+    def __init__(self, filename, library, mesh_id=None, name='', length_multiplier=1.0):
         super().__init__(mesh_id, name)
         self.filename = filename
         self._volumes = None
         self._centroids = None
         self.library = library
         self._output = True
+        self._specified_length_multiplier = False
+        self.length_multiplier = length_multiplier
 
     @property
     def filename(self):
@@ -713,6 +722,18 @@ class UnstructuredMesh(MeshBase):
                       Iterable, Real)
         self._centroids = centroids
 
+    @property
+    def length_multiplier(self):
+        return self._length_multiplier
+
+    @length_multiplier.setter
+    def length_multiplier(self, length_multiplier):
+        cv.check_type("Unstructured mesh length multiplier", length_multiplier, Real)
+        self._length_multiplier = length_multiplier
+
+        if (self._length_multiplier != 1.0):
+          self._specified_length_multiplier = True
+
     def __repr__(self):
         string = super().__repr__()
         string += '{: <16}=\t{}\n'.format('\tFilename', self.filename)
@@ -836,6 +857,9 @@ class UnstructuredMesh(MeshBase):
         subelement = ET.SubElement(element, "filename")
         subelement.text = self.filename
 
+        if (self._specified_length_multiplier):
+          element.set("length_multiplier", str(self.length_multiplier))
+
         return element
 
     @classmethod