Simplify conditional

test/test_check_arities.py

@@ -9,7 +9,9 @@
     TestFunction,
     TrialFunction,
     adjoint,
+    as_tensor,
     cofac,
+    conditional,
     conj,
     derivative,
     ds,
@@ -84,3 +86,23 @@ def test_product_arity():
     with pytest.raises(ArityMismatch):
         L = inner(v, v) * dx
         compute_form_data(L, complex_mode=False)
+
+
+def test_zero_simplify_arity():
+    cell = tetrahedron
+    D = Mesh(FiniteElement("Lagrange", cell, 1, (3,), identity_pullback, H1))
+    V = FunctionSpace(D, FiniteElement("Lagrange", cell, 2, (), identity_pullback, H1))
+    v = TestFunction(V)
+    u = Coefficient(V)
+
+    zero = as_tensor([0, u])[0]
+    F = inner(u, v + zero) * dx
+    compute_form_data(F, complex_mode=False)
+
+    zero = conditional(u < 0, 0, 0)
+    F = inner(u, v + zero) * dx
+    compute_form_data(F, complex_mode=False)
+
+    zero = conditional(u < 0, 0, conditional(u == 0, 0, 0))
+    F = inner(u, v + zero) * dx
+    compute_form_data(F, complex_mode=False)

ufl/conditional.py

@@ -264,10 +264,23 @@ class Conditional(Operator):
     In C++ these take the format `(condition ? true_value : false_value)`.
     """
 
-    __slots__ = ()
+    __slots__ = ("_initialised",)
+
+    def __new__(cls, condition, true_value, false_value):
+        """Create a new Conditional."""
+        # Simplify
+        if true_value == false_value:
+            return true_value
+        # Construct a new instance to be initialised
+        self = Operator.__new__(cls)
+        self._initialised = False
+        return self
 
     def __init__(self, condition, true_value, false_value):
         """Initialise."""
+        if self._initialised:
+            return
+        # Checks
         if not isinstance(condition, Condition):
             raise ValueError("Expecting condition as first argument.")
         true_value = as_ufl(true_value)
@@ -290,8 +303,8 @@ def __init__(self, condition, true_value, false_value):
                 )
             ):
                 raise ValueError("Non-scalar == or != is not allowed.")
-
         Operator.__init__(self, (condition, true_value, false_value))
+        self._initialised = True
 
     def evaluate(self, x, mapping, component, index_values):
         """Evaluate."""