## ●Hessian

いかにTeXとはいえ，これはめんどくさそーだなーと思っていたところ，案外楽でした。コピペで何とかなる：

\left[ \begin{array}{cccc}

\frac{\partial^2 \ell}{\partial \theta_1^2} &

\frac{\partial^2 \ell}{\partial \theta_1 \partial \theta_2} &

\cdots &

\frac{\partial^2 \ell}{\partial \theta_1 \partial \theta_k} \\

\frac{\partial^2 \ell}{\partial \theta_2 \partial \theta_1} &

\frac{\partial^2 \ell}{\partial \theta_2^2} &

\cdots &

\frac{\partial^2 \ell}{\partial \theta_2 \partial \theta_k} \\

\vdots & \vdots & \ddots & \vdots \\

\frac{\partial^2 \ell}{\partial \theta_k \partial \theta_1} &

\frac{\partial^2 \ell}{\partial \theta_k \partial \theta_2} &

\cdots & \frac{\partial^2 \ell}{\partial \theta_k^2}

\end{array} \right]