标签 eqnarray 拆分和对齐

Question

我有这个 tex 代码

\begin{eqnarray}
&\partial_{t}f =D \nabla^{2}f -f (1-f)[(1-s)-(2-s)f]\epsilon          \label{eqn:1}\\ \nonumber
&\\ 
\text{from which we get}
&\partial_{t}f =- \frac{\delta F}{\delta f} \\  \nonumber
&\\ 
\text{where f is} 
&F=\int dx \big[ \frac{1}{2} D (\partial_{x f^{2}})+ V(f)\big] \\     \nonumber
&\\ 
\text{and} 
& V(f) \equiv \int df f (1-f)[(1-s)-(2-s)f]\epsilon \\ \nonumber
&\\ 
&\hspace{0.8cm}  \equiv \frac{1}{2}f^{2}-\frac{1}{3}(3- 2s)f^{3}+\frac{1}{4}(2-s)f^{4}
\end{eqnarray}

我想要为其中一个方程式添加标签；我尝试使用对齐和拆分，但无法使它们对齐。

Answer 1

这些选项中是否有一个是您想要的？

\documentclass{article}
\usepackage{mathtools}

\usepackage{lipsum}
\begin{document}
\lipsum[66]
    \begin{align}
&&  \partial_{t}f   
    & = D \nabla^{2}f -f(1-f)[(1-s)-(2-s)f]\epsilon
                    \label{eqn:1}                   \\ 
&\text{from which we get}  
    & \partial_{t}f  
    & = -\frac{\delta F}{\delta f}                  \\  
& \text{where $f$ is} 
    & F
    & = \int dx \big[ \frac{1}{2} D (\partial_{x f^{2}})+ V(f)\big] \\
& \text{and}
    & V(f) 
    &   \equiv \int df f (1-f)[(1-s)-(2-s)f]\epsilon  \\
    &&& \equiv \frac{1}{2}f^{2}-\frac{1}{3}(3- 2s)f^{3} + \frac{1}{4}(2-s)f^{4}
    \end{align}
or better is to use \verb+\shortintertext{...}+ defined in the package \verb+mathtools+:
    \begin{align}
\partial_{t}f
    & = D \nabla^{2}f -f(1-f)[(1-s)-(2-s)f]\epsilon
                    \label{eqn:1}                   
\shortintertext{from which we get}
\partial_{t}f
    & = -\frac{\delta F}{\delta f}                 
\shortintertext{where $f$ is}
F   & = \int dx \big[ \frac{1}{2} D (\partial_{x f^{2}})+ V(f)\big]
\shortintertext{and}
V(f)& \equiv \int df f (1-f)[(1-s)-(2-s)f]\epsilon          \\
    & \equiv \frac{1}{2}f^{2}-\frac{1}{3}(3- 2s)f^{3} + \frac{1}{4}(2-s)f^{4}
\end{align}
\end{document}