latex公式插入换行+加数字

记录一下，使用aligned需要导入包：\usepackage{amsmath}

\begin{equation}
\begin{aligned}
{L_{N - pair}}\left( {x,{x^ + },\sum\limits_{i = 1}^{N - 1} {x_i^ - } ;f} \right) &= \log \left( {1 + \sum\limits_{i = 1}^{N - 1} {\exp \left( {f{{\left( x \right)}^T}f\left( {x_i^ - } \right) - f{{\left( x \right)}^T}f\left( {{x^ + }} \right)} \right)} } \right)  \\
&=  - \log \frac{{\exp \left( {f{{\left( x \right)}^T}f\left( {{x^ + }} \right)} \right)}}{{\exp \left( {f{{\left( x \right)}^T}f\left( {{x^ + }} \right)} \right){\rm{ + }}\sum\nolimits_{i = 1}^{N - 1} {\exp \left( {f{{\left( x \right)}^T}f\left( {x_i^ - } \right)} \right)} }}
\end{aligned}
\end{equation}