diff --git a/CHANGELOG.md b/CHANGELOG.md
index e5884a48b8..7d5855bb19 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -36,6 +36,7 @@ example notebook ([#1602](https://github.com/pybamm-team/PyBaMM/pull/1602))
 
 ## Bug fixes
 
+-   Updated documentation to include some previously missing functions, such as `erf` and `tanh` ([#1628](https://github.com/pybamm-team/PyBaMM/pull/1628))
 -   Fixed reading citation file without closing ([#1620](https://github.com/pybamm-team/PyBaMM/pull/1620))
 -   Porosity variation for SEI and plating models is calculated from the film thickness rather than from a separate ODE ([#1617](https://github.com/pybamm-team/PyBaMM/pull/1617))
 -   Fixed a bug where the order of the indexing for the entries of variables discretised using FEM was incorrect ([#1556](https://github.com/pybamm-team/PyBaMM/pull/1556))
diff --git a/docs/source/expression_tree/functions.rst b/docs/source/expression_tree/functions.rst
index 4ffecf4b68..17f79c7692 100644
--- a/docs/source/expression_tree/functions.rst
+++ b/docs/source/expression_tree/functions.rst
@@ -7,6 +7,16 @@ Functions
 .. autoclass:: pybamm.SpecificFunction
   :members:
 
+.. autoclass:: pybamm.Arcsinh
+  :members:
+
+.. autofunction:: pybamm.arcsinh
+
+.. autoclass:: pybamm.Arctan
+  :members:
+
+.. autofunction:: pybamm.arctan
+
 .. autoclass:: pybamm.Cos
   :members:
 
@@ -17,6 +27,13 @@ Functions
 
 .. autofunction:: pybamm.cosh
 
+.. autoclass:: pybamm.Erf
+  :members:
+
+.. autofunction:: pybamm.erf
+
+.. autofunction:: pybamm.erfc
+
 .. autoclass:: pybamm.Exponential
   :members:
 
@@ -27,10 +44,20 @@ Functions
 
 .. autofunction:: pybamm.log
 
+.. autofunction:: pybamm.log10
+
+.. autoclass:: pybamm.Max
+  :members:
+
 .. autofunction:: pybamm.max
 
+.. autoclass:: pybamm.Min
+  :members:
+
 .. autofunction:: pybamm.min
 
+.. autofunction:: pybamm.sech
+
 .. autoclass:: pybamm.Sin
   :members:
 
@@ -40,3 +67,13 @@ Functions
   :members:
 
 .. autofunction:: pybamm.sinh
+
+.. autoclass:: pybamm.Sqrt
+  :members:
+
+.. autofunction:: pybamm.sqrt
+
+.. autoclass:: pybamm.Tanh
+  :members:
+
+.. autofunction:: pybamm.tanh
diff --git a/pybamm/expression_tree/functions.py b/pybamm/expression_tree/functions.py
index cb8252a76c..ebe2cfd356 100644
--- a/pybamm/expression_tree/functions.py
+++ b/pybamm/expression_tree/functions.py
@@ -311,6 +311,22 @@ def arcsinh(child):
     return simplified_function(Arcsinh, child)
 
 
+class Arctan(SpecificFunction):
+    """Arctan function."""
+
+    def __init__(self, child):
+        super().__init__(np.arctan, child)
+
+    def _function_diff(self, children, idx):
+        """See :meth:`pybamm.Function._function_diff()`."""
+        return 1 / (children[0] ** 2 + 1)
+
+
+def arctan(child):
+    """Returns hyperbolic tan function of child."""
+    return simplified_function(Arctan, child)
+
+
 class Cos(SpecificFunction):
     """Cosine function."""
 
@@ -343,6 +359,27 @@ def cosh(child):
     return simplified_function(Cosh, child)
 
 
+class Erf(SpecificFunction):
+    """Error function."""
+
+    def __init__(self, child):
+        super().__init__(special.erf, child)
+
+    def _function_diff(self, children, idx):
+        """See :meth:`pybamm.Function._function_diff()`."""
+        return 2 / np.sqrt(np.pi) * Exponential(-children[0] ** 2)
+
+
+def erf(child):
+    """Returns error function of child."""
+    return simplified_function(Erf, child)
+
+
+def erfc(child):
+    """Returns complementary error function of child."""
+    return 1 - simplified_function(Erf, child)
+
+
 class Exponential(SpecificFunction):
     """Exponential function."""
 
@@ -491,40 +528,3 @@ def _function_diff(self, children, idx):
 def tanh(child):
     """Returns hyperbolic tan function of child."""
     return simplified_function(Tanh, child)
-
-
-class Arctan(SpecificFunction):
-    """Arctan function."""
-
-    def __init__(self, child):
-        super().__init__(np.arctan, child)
-
-    def _function_diff(self, children, idx):
-        """See :meth:`pybamm.Function._function_diff()`."""
-        return 1 / (children[0] ** 2 + 1)
-
-
-def arctan(child):
-    """Returns hyperbolic tan function of child."""
-    return simplified_function(Arctan, child)
-
-
-class Erf(SpecificFunction):
-    """Error function."""
-
-    def __init__(self, child):
-        super().__init__(special.erf, child)
-
-    def _function_diff(self, children, idx):
-        """See :meth:`pybamm.Function._function_diff()`."""
-        return 2 / np.sqrt(np.pi) * Exponential(-children[0] ** 2)
-
-
-def erf(child):
-    """Returns error function of child."""
-    return simplified_function(Erf, child)
-
-
-def erfc(child):
-    """Returns complementary error function of child."""
-    return 1 - simplified_function(Erf, child)