测试LaTeX公式输入：

此文档仅用于测试该博客系统能否接受数学公式输入。
$$2^{3}+5$$

$$2^{3}+5$$

接下来测试复杂公式的输入：

$$\mathbf{X} = \left( \begin{array}{ccc} x_{11} & x_{12} & \ldots \ x_{21} & x_{22} & \ldots \ \vdots & \vdots & \ddots \end{array} \right)$$

$$\mathop{\mathrm{corr}}(X,Y)= \frac{\displaystyle \sum_{i=1}^n(x_i-\overline x) (y_i-\overline y)} {\displaystyle\biggl[ \sum_{i=1}^n(x_i-\overline x)^2 \sum_{i=1}^n(y_i-\overline y)^2 \biggr]^{1/2}} $$

分段函数：

$$ y = \left{ \begin{array}{ll} a & \textrm{if $d>c$}\ b+x & \textrm{in the morning}\ l & \textrm{all day long} \end{array} \right. $$

$$\newcommand{\ud}{\mathrm{d}} \int!!!\int_{D} g(x,y) , \ud x, \ud y \ $$

instead of

$$ \\int\int_{D} g(x,y)\ud x \ud y$$

等号对齐：

$$\begin{eqnarray} f(x) & = & \cos x \ f’(x) & = & -\sin x \ \int_{0}^{x} f(y)dy & = & \sin x \end{eqnarray}$$