如何让对齐或类似的方程环境使用整条线而不是以等号为中心

Question

我正在创建一个 Beamer 演示文稿，其中方程式环境中的一条线应填满整个屏幕，而不应仅以等号为中心。我认为这看起来更美观，观众也更容易阅读。实际上，只使用\multline一行就可以实现这一点。我如何在\align或任何其他“方程式对齐”环境中实现这种行为？这是一个比较，我想通过如下所示的对齐来实现上述效果：

\documentclass{beamer}
\usepackage{amsmath}
\usepackage[thicklines]{cancel}
\usepackage{color} 
\definecolor{Blue}{rgb}{0,0,1}
\definecolor{Red}{rgb}{1,0,0}
\newcommand{\ccancel}[2]{\renewcommand{\CancelColor}{\color{#2}}\bcancel{#1}}

\begin{document}
\begin{frame}
\begin{multline*}
                                    \frac{\partial s_{\mu}}{\partial x_\mu}=
                                    A \;[\ccancel{ \frac{\partial \phi^*}{\partial x_{\mu}}
                                    \frac{\partial \phi}{\partial x_{\mu}}}{Red}
                                    -\ccancel{\vphantom{\frac{1}{1}}(\square \phi^*)\phi}{Blue} 
                                    +\ccancel{\vphantom{\frac{1}{1}(kk)}\phi^* \square\phi}{Blue} 
                                    -\ccancel{\frac{\partial \phi^*}{\partial x_{\mu}}
                                    \frac{\partial \phi}{\partial x_{\mu}}}{Red}] 
\end{multline*}
\\[2em]
\begin{align*}
            \frac{\partial s_{\mu}}{\partial x_\mu} & = A \;[\ccancel{ \frac{\partial \phi^*}{\partial x_{\mu}}
                                    \frac{\partial \phi}{\partial x_{\mu}}}{Red}
                                    -\ccancel{\vphantom{\frac{1}{1}}(\square \phi^*)\phi}{Blue} 
                                    +\ccancel{\vphantom{\frac{1}{1}(kk)}\phi^* \square\phi}{Blue} 
                                    -\ccancel{\frac{\partial \phi^*}{\partial x_{\mu}}
                                    \frac{\partial \phi}{\partial x_{\mu}}}{Red}] \\
                                                    & = 0 
    \end{align*}

\end{frame}
\end{document}

Answer 1

我不太喜欢取消符号。不过这里有一个建议；请注意，我定义了两个新命令：一个用于简化输入，另一个用于获得拉普拉斯算子的正确间距。

\documentclass{beamer}
\usepackage{amsmath}
\usepackage[thicklines]{cancel}
\usepackage{color} 
\definecolor{Blue}{rgb}{0,0,1}
\definecolor{Red}{rgb}{1,0,0}
\newcommand{\ccancel}[2]{\renewcommand{\CancelColor}{\color{#2}}\bcancel{#1}}
\newcommand{\pder}[2]{\frac{\partial#1}{\partial#2}}
\DeclareMathOperator{\lapl}{\square}

\begin{document}
\begin{frame}
\begin{align*}
\pder{s_{\mu}}{x_\mu} &=
   A\biggl[
     \ccancel{\pder{\phi^*}{x_{\mu}}\pder{\phi}{x_{\mu}}}{Red}
    -\ccancel{\vphantom{\dfrac{1}{1}}\bigl(\lapl\phi^*\bigr)\phi}{Blue} 
    +\!\ccancel{\hphantom{\big(}\vphantom{\dfrac{1}{1}}\phi^*\lapl\phi\hphantom{\big)}}{Blue}\!
    -\ccancel{\pder{\phi^*}{x_{\mu}}\pder{\phi}{x_{\mu}}}{Red}
  \biggr]
\\[3ex]
&=0
\end{align*}

\end{frame}
\end{document}

我还做了一些调整以获得与蓝色条相同的倾斜度。

Answer 2

我必须同意 Herbert 的观点，原因有二：i）术语的位置确实可能更具可读性，但也更模糊；ii）小括号看起来像是使部分表达式等于的条件，A而你提醒它类似于a(t)=b(t) [almost everywhere]

我建议以下做法，其中取消效果稍微明显一些并且无颜色。

\documentclass{beamer}
\usepackage{mathtools,lmodern,xcolor}


\definecolor{Blue}{rgb}{0,0,1}
\definecolor{Red}{rgb}{1,0,0}
\newcommand{\ccancel}[2]{\renewcommand{\CancelColor}{\color{#2}}\bcancel{#1}}

\begin{document}
\begin{frame}

\begin{align*}
\frac{\partial s_{\mu}}{\partial x_\mu} & = A \left(
              \underbracket[0.5pt][3pt]{\frac{\partial \phi^*}{\partial x_{\mu}}\frac{\partial \phi}{\partial x_{\mu}}
             -\underbracket[0.5pt][3pt]{\vphantom{\frac{\partial}{\partial_\mu}}\square \phi^*\phi+\phi^* \square\phi}_{0}{}
             -\frac{\partial \phi^*}{\partial x_{\mu}}\frac{\partial \phi}{\partial x_{\mu}}}_{0}\right) \\[2em]
    & = 0 
    \end{align*}

\end{frame}
\end{document}