Fix Taylor expansion documentation
@@ -681,7 +681,7 @@ approximated as follows:
.. note::
Briefly, a first-order Taylor approximation says that
- :math:`l(z) \approx l(a) + (z - a) \frac{\partial l(a)}{\partial a}`.
+ :math:`l(z) \approx l(a) + (z - a) \frac{\partial l}{\partial z}(a)`.
Here, :math:`z` corresponds to :math:`F_{m - 1}(x_i) + h_m(x_i)`, and
:math:`a` corresponds to :math:`F_{m-1}(x_i)`
