数组——动态！{decl.} 参数

Question

我使用!{=}数组来构建紧凑方程，但在最后一行，我希望使用\approx而不是=。

是否可以 ？

\documentclass{standalone}

\usepackage{array,tabularx}

\begin{document}

$\begin{array}{r!{=}l}
    TS  &TU \times\cos\hat{T} \\
        &7.5\times\cos\,41.5\\
        &5.6\\ % \approx here instead of =
\end{array}$

\end{document}

Answer 1

我不确定这是否真的节省时间。

\documentclass[border=2]{standalone}

\usepackage{array}

\newcommand{\noeq}[1]{\multicolumn{1}{r!{#1}}{}}

\begin{document}

$\begin{array}{r!{=}l}
TS             &TU \times\cos\hat{T} \\
               &7.5\times\cos 41.5 \\
\noeq{\approx} &5.6
\end{array}$

\end{document}

我会这样做；请注意，间距是关系符号周围的正常间距。

\documentclass[border=2]{standalone}

\usepackage{array}

\begin{document}

$\begin{array}{r@{}>{{}}l}
TS &= TU \times\cos\hat{T} \\
   &= 7.5\times\cos 41.5 \\
   &\approx 5.6
\end{array}$

\end{document}

这可能更有吸引力，因为它会自动照顾两侧的空间。

\documentclass[border=2]{standalone}

\usepackage{amsmath}

\begin{document}

$\begin{aligned}
TS &= TU \times\cos\hat{T} \\
   &= 7.5\times\cos 41.5 \\
   &\approx 5.6
\end{aligned}$

\end{document}

Answer 2

为了获得额外的灵活性，请考虑创建一个 3 列array，其中中间列包含关系运算符 ——=或者\approx。

\documentclass{article}
\usepackage{array} % for "\newcolumntype" macro
\newcolumntype{C}{>{{}}c<{{}}}
\begin{document}

$\setlength\arraycolsep{0pt}
  \begin{array}{rCl}
     TS &=&TU \times\cos\hat{T} \\
        &=&7.5\times\cos\,41.5\\
        &\approx&5.6 
  \end{array}$
\end{document}

Answer 3

\documentclass{standalone}

\usepackage{array}

\newif\ifUseApprox
\protected\def\Equal{\ifUseApprox\approx\else=\fi}
\def\EqualUseApprox{\global\UseApproxtrue}
\def\EqualUseEqual {\global\UseApproxfalse}

\begin{document}

$\begin{array}{r!{\Equal}l}
    TS  &TU \times\cos\hat{T} \\
        &7.5\times\cos\,41.5\\
   \EqualUseApprox     &5.6\\ % \approx here instead of =
\end{array}$

\end{document}

\documentclass[varwidth, border=10pt]{standalone}

\usepackage{array, shortvrb}

\newif\ifUseApprox
\protected\def\Equal{\ifUseApprox\approx\else=\fi}
\def\EqualUseApprox{\global\UseApproxtrue}
\def\EqualUseEqual {\global\UseApproxfalse}

\begin{document}
\hsize 6cm

$\begin{array}{r!{\Equal}l}
    TS  &TU \times\cos\hat{T} \\
        &7.5\times\cos\,41.5\\
   \EqualUseApprox     &5.6\\ % \approx here instead of =
\end{array}$

I now want to have a line \verb|\approx 7.5\times 0.75| 
followed by a line with \verb|= 5.63| !

\EqualUseEqual % reset

$\begin{array}{r!{\Equal}l}
    TS  &TU \times\cos\hat{T} \\
        &7.5\times\cos\,41.5\\
   \EqualUseApprox     &5.6\\ % \approx here instead of =
        &7.5\times 0.75\\
   \EqualUseEqual      &5.63\\ % again using =
\end{array}$

\end{document}