PR FEniCS#184: fix behaviour when perp is Zero and expand testing

test/test_tensoralgebra.py

@@ -106,11 +106,25 @@ def test_cross(self):
 
 
 def test_perp(self):
+    # Test perp is generally doing the correct thing
     u = as_vector([3, 1])
     v = perp(u)
     w = as_vector([-1, 3])
     self.assertEqualValues(v, w)
 
+    # Test that a perp does the correct thing to Zero
+    u = zero(2)
+    v = perp(u)
+    self.assertEqualValues(u, v)
+
+    # Test that perp throws an error if the wrong thing is provided
+    u = as_vector([3, 1, -1])  # 3D vector instead of 2D
+    with pytest.raises(ValueError):
+        v = perp(u)
+    u = as_matrix([[1, 3], [0, 4]])  # Matrix instead of vector
+    with pytest.raises(ValueError):
+        v = perp(u)
+
 
 def xtest_dev(self, A):
     C = dev(A)

ufl/tensoralgebra.py

@@ -232,7 +232,7 @@ def __new__(cls, A):
 
         # Simplification
         if isinstance(A, Zero):
-            return Zero((), A.ufl_free_indices, A.ufl_index_dimensions)
+            return Zero(sh, A.ufl_free_indices, A.ufl_index_dimensions)
 
         return CompoundTensorOperator.__new__(cls)