\begin{equation*} \frac{1}{m}\ \Sigma_{i=1}^{m}\ w^{(i)}_{x}\ [\ \frac{\partial c}{\partial \eta_{k}} (\Theta x^{(i)}, \Lambda)\ \frac{\partial \eta_{k}}{\partial \theta_{kj}} - x_{j}^{(i)}\ [\Lambda\ T(y^{(i)})]_{k}\ ]\ +\ \lambda \theta_{kj} \end{equation*}