$$H（F）=\left[\begin{array}{cccc}\frac{{\partial }^{2}F}{\partial X_1^2}& \frac{{\partial }^{2}F}{\partial X_1\partial X_2}& \cdots & \frac{{\partial }^{2}F}{\partial X_1\partial X_N}\\ \frac{{\partial }^{2}F}{\partial X_2\partial X_1}& \frac{{\partial }^{2}F}{\partial X_2^2}& \cdots & \frac{{\partial }^{2}F}{\partial X_2\partial X_N}\\ ⋮& ⋮& \ddots & ⋮\\ \frac{{\partial }^{2}F}{\partial X_N\partial X_1}& \frac{{\partial }^{2}F}{\partial X_N\partial X_2}& \cdots & \frac{{\partial }^{2}F}{\partial X_N^2}\end{array}\right]$$