Implement empty() for BaseForm subclasses

ufl/algorithms/formsplitter.py

@@ -10,6 +10,8 @@
 
 from typing import Optional
 
+import numpy as np
+
 from ufl.algorithms.map_integrands import map_expr_dag, map_integrand_dags
 from ufl.argument import Argument
 from ufl.classes import FixedIndex, ListTensor
@@ -53,14 +55,10 @@ def argument(self, obj):
                 Q_i = FunctionSpace(dom, sub_elem)
                 a = Argument(Q_i, obj.number(), part=obj.part())
 
-                indices = [()]
-                for m in a.ufl_shape:
-                    indices = [(*k, j) for k in indices for j in range(m)]
-
                 if i == self.idx[obj.number()]:
-                    args.extend(a[j] for j in indices)
+                    args.extend(a[j] for j in np.ndindex(a.ufl_shape))
                 else:
-                    args.extend(Zero() for j in indices)
+                    args.extend(Zero() for j in np.ndindex(a.ufl_shape))
 
             return as_vector(args)
 

ufl/form.py

@@ -120,6 +120,10 @@ def ufl_domain(self):
         # Return the one and only domain
         return domain
 
+    def empty(self):
+        """Returns whether the BaseForm has no components."""
+        return False
+
     # --- Operator implementations ---
 
     def __eq__(self, other):
@@ -307,7 +311,7 @@ def integrals_by_domain(self, domain):
 
     def empty(self):
         """Returns whether the form has no integrals."""
-        return self.integrals() == ()
+        return len(self.integrals()) == 0
 
     def ufl_domains(self):
         """Return the geometric integration domains occuring in the form.
@@ -812,6 +816,10 @@ def equals(self, other):
             a == b for a, b in zip(self.components(), other.components())
         )
 
+    def empty(self):
+        """Returns whether the FormSum has no components."""
+        return len(self.components()) == 0
+
     def __str__(self):
         """Compute shorter string representation of form. This can be huge for complicated forms."""
         # Warning used for making sure we don't use this in the general pipeline: