Scalar field zero treatment

Author: Michael Jung

src/sage/manifolds/differentiable/automorphismfield.py

@@ -247,7 +247,7 @@ def _del_derived(self):
         # then deletes the inverse automorphism:
         self._inverse = None
 
-    def set_comp(self, basis=None, **kwargs):
+    def set_comp(self, basis=None):
         r"""
         Return the components of ``self`` w.r.t. a given module basis for
         assignment.
@@ -319,7 +319,7 @@ class :class:`~sage.tensor.modules.comp.Components`; if such
                                  "changed")
         return TensorField._set_comp_unsafe(self, basis=basis)
 
-    def add_comp(self, basis=None, **kwargs):
+    def add_comp(self, basis=None):
         r"""
 
         Return the components of ``self`` w.r.t. a given module basis for

src/sage/manifolds/differentiable/tensorfield_paral.py

@@ -886,7 +886,7 @@ class :class:`~sage.tensor.modules.comp.Components`; if such
 
         if basis._domain == self._domain:
             # Setting components on the tensor field domain:
-            return FreeModuleTensor.set_comp(self, basis=basis, **kwargs)
+            return FreeModuleTensor.set_comp(self, basis=basis)
 
         # Setting components on a subdomain:
         #

src/sage/manifolds/scalarfield.py

@@ -1673,12 +1673,29 @@ def set_expr(self, coord_expression, chart=None):
             sage: f._express # the (u,v) expression has been lost:
             {Chart (M, (x, y)): 3*y}
 
+        Since zero and one are special elements, their components cannot be
+        changed::
+
+            sage: z = M.zero_scalar_field()
+            sage: z.set_expr(3*y)
+            Traceback (most recent call last):
+            ...
+            AssertionError: the components of the element zero cannot be changed
+            sage: one = M.one_scalar_field()
+            sage: one.set_expr(3*y)
+            Traceback (most recent call last):
+            ...
+            AssertionError: the components of the element 1 cannot be changed
+
         """
+        if self is self.parent().one() or self is self.parent().zero():
+            raise AssertionError("the components of the element "
+                                 "{} cannot be changed".format(self._name))
         if chart is None:
             chart = self._domain._def_chart
-        self._is_zero = False # a priori
         self._express.clear()
         self._express[chart] = chart.function(coord_expression)
+        self._is_zero = False # a priori
         self._del_derived()
 
     def add_expr(self, coord_expression, chart=None):
@@ -1718,7 +1735,24 @@ def add_expr(self, coord_expression, chart=None):
             sage: f._express # random (dict. output); f has now 2 expressions:
             {Chart (M, (x, y)): 3*y, Chart (M, (u, v)): cos(u) - sin(v)}
 
+        Since zero and one are special elements, their components cannot be
+        changed::
+
+            sage: z = M.zero_scalar_field()
+            sage: z.add_expr(cos(u)-sin(v), c_uv)
+            Traceback (most recent call last):
+            ...
+            AssertionError: the components of the element zero cannot be changed
+            sage: one = M.one_scalar_field()
+            sage: one.add_expr(cos(u)-sin(v), c_uv)
+            Traceback (most recent call last):
+            ...
+            AssertionError: the components of the element 1 cannot be changed
+
         """
+        if self is self.parent().one() or self is self.parent().zero():
+            raise AssertionError("the components of the element "
+                                 "{} cannot be changed".format(self._name))
         if chart is None:
             chart = self._domain._def_chart
         self._express[chart] = chart.function(coord_expression)