add create_reference function

Author: mscroggs

symfem/__init__.py

@@ -32,32 +32,44 @@
                 _elementlist[_cell_class][_n] = _element
 
 
-def create_element(cell_type, element_type, order):
-    """Make a finite element.
+def create_reference(cell_type):
+    """Make a reference cell.
 
     Parameters
     ----------
     cell_type : str
         The reference cell type.
         Supported values: interval, triangle, quadrilateral, tetrahedron, hexahedron
-    element_type: str
-        The type of the element.
-    order: int
-        The order of the element.
     """
     if cell_type == "interval":
-        reference = _references.Interval()
+        return _references.Interval()
     elif cell_type == "triangle":
-        reference = _references.Triangle()
+        return _references.Triangle()
     elif cell_type == "tetrahedron":
-        reference = _references.Tetrahedron()
+        return _references.Tetrahedron()
     elif cell_type == "quadrilateral":
-        reference = _references.Quadrilateral()
+        return _references.Quadrilateral()
     elif cell_type == "hexahedron":
-        reference = _references.Hexahedron()
+        return _references.Hexahedron()
     else:
         raise ValueError(f"Unknown cell type: {cell_type}")
 
+
+def create_element(cell_type, element_type, order):
+    """Make a finite element.
+
+    Parameters
+    ----------
+    cell_type : str
+        The reference cell type.
+        Supported values: interval, triangle, quadrilateral, tetrahedron, hexahedron
+    element_type: str
+        The type of the element.
+    order: int
+        The order of the element.
+    """
+    reference = create_reference(cell_type)
+
     if reference.simplex:
         if element_type in _elementlist["simplex"]:
             return _elementlist["simplex"][element_type](reference, order)