Define FacetArea(interval) == 1.0 in geometry lowering.

ufl/algorithms/apply_geometry_lowering.py

@@ -40,7 +40,8 @@
                          ReferenceNormal,
                          ReferenceCellVolume, ReferenceFacetVolume,
                          CellVolume, FacetArea,
-                         SpatialCoordinate)
+                         SpatialCoordinate,
+                         FloatValue)
 # FacetJacobianInverse,
 # FacetOrientation, QuadratureWeight,
 
@@ -142,6 +143,7 @@ def facet_jacobian_determinant(self, o):
             return o
 
         domain = o.ufl_domain()
+        #tdim = domain.topological_dimension()
         FJ = self.facet_jacobian(FacetJacobian(domain))
         detFJ = determinant_expr(FJ)
 
@@ -209,12 +211,17 @@ def facet_area(self, o):
             return o
 
         domain = o.ufl_domain()
+        tdim = domain.topological_dimension()
         if not domain.is_piecewise_linear_simplex_domain():
             # Don't lower for non-affine cells, instead leave it to
             # form compiler
             warning("Only know how to compute the facet area of an affine cell.")
             return o
 
+        # Area of "facet" of interval (i.e. "area" of a vertex) is defined as 1.0
+        if tdim == 1:
+            return FloatValue(1.0)
+
         r = self.facet_jacobian_determinant(FacetJacobianDeterminant(domain))
         r0 = ReferenceFacetVolume(domain)
         return abs(r * r0)