#858 add vectordot and state_vectordot to api docs

Author: martinjrobins

docs/source/expression_tree/state_vector.rst

@@ -3,3 +3,6 @@ State Vector
 
 .. autoclass:: pybamm.StateVector
   :members:
+
+.. autoclass:: pybamm.StateVectorDot
+  :members:

docs/source/expression_tree/variable.rst

@@ -4,5 +4,9 @@ Variable
 .. autoclass:: pybamm.Variable
   :members:
 
+.. autoclass:: pybamm.VariableDot
+  :members:
+
 .. autoclass:: pybamm.ExternalVariable
   :members:
+

pybamm/expression_tree/symbol.py

@@ -486,10 +486,10 @@ def diff(self, variable):
         elif any(variable.id == x.id for x in self.pre_order()):
             return self._diff(variable)
         elif variable.id == pybamm.t.id and \
-            any(
-                isinstance(x, (pybamm.VariableBase, pybamm.StateVectorBase))
-                for x in self.pre_order()
-            ):
+                any(
+                    isinstance(x, (pybamm.VariableBase, pybamm.StateVectorBase))
+                    for x in self.pre_order()
+                ):
             return self._diff(variable)
         else:
             return pybamm.Scalar(0)