WIP: think about adding a distance_to_point_c function

FIAT/reference_element.py

@@ -527,7 +527,7 @@ def contains_point(self, point, epsilon=0):
         Whilst this could use `distance_to_point` in this function,
         `distance_to_point` cannot be used to return a symbolic expression so
         we have to reimplement the logic here. If this function is changed, be
-        sure to update `distance_to_point` as well.
+        sure to update `distance_to_point` and `distance_to_point_c` as well.
         """
         result = (sum(point) - epsilon <= 1)
         for c in point:
@@ -694,6 +694,23 @@ def __init__(self):
                     1: edges}
         super(UFCInterval, self).__init__(LINE, verts, topology)
 
+    def distance_to_point_c(self, point):
+        """Return a C expression which is equivalent to `distance_to_point`.
+
+        Assumes that one has imported `PetscRealPart`.
+
+        Parameters
+        ----------
+        point : str
+            The C expression for the point.
+
+        Returns
+        -------
+        str
+            The C expression for the distance to the point.
+        """
+        NotImplemented
+
 
 class DefaultTriangle(Simplex):
     """This is the reference triangle with vertices (-1.0,-1.0),