#858 time derivative of state vector gives state vector dot, raise errors if taking time derivative of *Dot classes

Author: martinjrobins

pybamm/expression_tree/state_vector.py

@@ -256,7 +256,12 @@ def _base_evaluate(self, t=None, y=None, y_dot=None, u=None):
         return out
 
     def _jac(self, variable):
-        if isinstance(variable, pybamm.StateVector):
+        if variable.id == pybamm.t.id:
+            return StateVectorDot(*self._y_slices, name=self.name + "'",
+                                  domain=self.domain,
+                                  auxiliary_domains=self.auxiliary_domains,
+                                  evaluation_array=self.evaluation_array)
+        elif isinstance(variable, pybamm.StateVector):
             return self._jac_same_vector(variable)
         elif isinstance(variable, pybamm.StateVectorDot):
             return self._jac_diff_vector(variable)
@@ -312,6 +317,10 @@ def _base_evaluate(self, t=None, y=None, y_dot=None, u=None):
         return out
 
     def _jac(self, variable):
+        if variable.id == pybamm.t.id:
+            raise pybamm.ModelError(
+                "cannot take second time derivative of a state vector"
+            )
         if isinstance(variable, pybamm.StateVectorDot):
             return self._jac_same_vector(variable)
         elif isinstance(variable, pybamm.StateVector):

pybamm/expression_tree/variable.py

@@ -48,9 +48,9 @@ def _evaluate_for_shape(self):
         )
 
     def _jac(self, variable):
-        if variable == self:
+        if variable.id == self.id:
             return pybamm.Scalar(1)
-        elif variable == pybamm.t:
+        elif variable.id == pybamm.t.id:
             return pybamm.VariableDot(self.name+"'",
                                       domain=self.domain,
                                       auxiliary_domains=self.auxiliary_domains)
@@ -99,6 +99,14 @@ def get_variable(self):
                         domain=self._domain,
                         auxiliary_domains=self._auxiliary_domains)
 
+    def _jac(self, variable):
+        if variable.id == self.id:
+            return pybamm.Scalar(1)
+        elif variable.id == pybamm.t.id:
+            raise pybamm.ModelError("cannot take second time derivative of a Variable")
+        else:
+            return pybamm.Scalar(0)
+
 
 class ExternalVariable(Variable):
     """A node in the expression tree representing an external variable variable
@@ -161,3 +169,13 @@ def _base_evaluate(self, t=None, y=None, y_dot=None, u=None):
         # raise more informative error if can't find name in dict
         except KeyError:
             raise KeyError("External variable '{}' not found".format(self.name))
+
+    def _jac(self, variable):
+        if variable.id == self.id:
+            return pybamm.Scalar(1)
+        elif variable.id == pybamm.t.id:
+            raise pybamm.ModelError("cannot take time derivative of an external variable")
+        else:
+            return pybamm.Scalar(0)
+
+