测试多行latex

\[\begin{align} M_{per}&=M_{ortho}M_{persp\rightarrow -ortho}\\\\ &=\begin{bmatrix}\frac{2}{r-l}& 0& 0& -\frac{r+l}{r-l}\\ 0& \frac{2}{t-b}& 0& -\frac{t+b}{t-b}\\ 0& 0& \frac{2}{n-f}& -\frac{n+f}{n-f}\\ 0& 0& 0& 1\end{bmatrix}\begin{bmatrix}n& 0& 0& 0\\ 0& n& 0& 0\\ 0& 0& n+f& -nf\\ 0& 0& 1& 0\end{bmatrix}\\\\ &=\begin{bmatrix}\frac{2n}{r-l}& 0&\frac{l+r}{l-r}& 0\\ 0& \frac{2n}{t-b}& \frac{b+t}{b-t}& 0\\ 0& 0& \frac{f+n}{n-f}& \frac{2fn}{f-n}\\ 0& 0& 1& 0\end{bmatrix} \end{align}\]