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# 数学模式中的间距

本文介绍如何在数学模式中插入不同宽度的空格。

## 引言

在某些情况下，调整（La）TeX 的默认数学模式间距会很有用；让我们看一个示例：

```latex
\documentclass{article}
\usepackage{amssymb}
\begin{document}
假设我们有如下集合
\[
S = \{ z \in \mathbb{C}\, |\, |z| < 1 \} \quad \textrm{and} \quad S_2=\partial{S}
\]
\end{document}
```

[在 Overleaf 中打开此示例](https://www.overleaf.com/docs?engine=pdflatex\&snip_name=Math+mode+spacing+example\&snip=%5Cdocumentclass%7Barticle%7D%0A%5Cusepackage%7Bamssymb%7D%0A%5Cbegin%7Bdocument%7D%0AAssume+we+have+the+next+sets%0A%5C%5B%0AS+%3D+%5C%7B+z+%5Cin+%5Cmathbb%7BC%7D%5C%2C+%7C%5C%2C+%7Cz%7C+%3C+1+%5C%7D+%5Cquad+%5Ctextrm%7Band%7D+%5Cquad+S_2%3D%5Cpartial%7BS%7D%0A%5C%5D%0A%5Cend%7Bdocument%7D)

此示例生成如下输出：

![展示数学间距调整的示例](/files/8b764ae4c5d456bd3cb6f81ea0441abd87ea1385)

如你在这个示例中所见，可以通过一些特殊命令显式地调整数学文本的间距。

## 空格

下面的示例包含使用各种命令插入的空格完整列表，并演示它们对排版数学公式的影响。

```latex
\documentclass{article}
\usepackage{amsmath}
\begin{document}
数学模式中的空格。

\begin{align*}
f(x) &= x^2\! +3x\! +2 \\
f(x) &= x^2+3x+2 \\
f(x) &= x^2\, +3x\, +2 \\
f(x) &= x^2\: +3x\: +2 \\
f(x) &= x^2\; +3x\; +2 \\
f(x) &= x^2\ +3x\ +2 \\
f(x) &= x^2\quad +3x\quad +2 \\
f(x) &= x^2\qquad +3x\qquad +2
\end{align*}
\end{document}
```

[在 Overleaf 中打开此示例](https://www.overleaf.com/docs?engine=pdflatex\&snip_name=Math+mode+spacing+example\&snip=%5Cdocumentclass%7Barticle%7D%0A%5Cusepackage%7Bamsmath%7D%0A%5Cbegin%7Bdocument%7D%0ASpaces+in+mathematical+mode.%0A%0A%5Cbegin%7Balign%2A%7D%0Af%28x%29+%26%3D+x%5E2%5C%21+%2B3x%5C%21+%2B2+%5C%5C%0Af%28x%29+%26%3D+x%5E2%2B3x%2B2+%5C%5C%0Af%28x%29+%26%3D+x%5E2%5C%2C+%2B3x%5C%2C+%2B2+%5C%5C%0Af%28x%29+%26%3D+x%5E2%5C%3A+%2B3x%5C%3A+%2B2+%5C%5C%0Af%28x%29+%26%3D+x%5E2%5C%3B+%2B3x%5C%3B+%2B2+%5C%5C%0Af%28x%29+%26%3D+x%5E2%5C+%2B3x%5C+%2B2+%5C%5C%0Af%28x%29+%26%3D+x%5E2%5Cquad+%2B3x%5Cquad+%2B2+%5C%5C%0Af%28x%29+%26%3D+x%5E2%5Cqquad+%2B3x%5Cqquad+%2B2%0A%5Cend%7Balign%2A%7D%0A%5Cend%7Bdocument%7D)

此示例生成如下输出：

![数学模式中调整间距的更多示例](/files/d2426418ddffa66c3a52b45cdbf0195626ec8e85)

请查看 [参考指南](#reference-guide) 以了解这些命令的说明。

**注意**：要查看以下内容的说明 `align*` 环境，请参见 [使用 amsmath 对齐方程](/latex/zh-cn/shu-xue/06-aligning-equations-with-amsmath.md)

## 运算符间距

数学模式中运算符和关系符号周围的间距由特定的跳距宽度控制：

* `\thinmuskip` （默认情况下它等于 3 mu）
* `\medmuskip` （默认情况下它等于 4 mu）
* `\thickmuskip` （默认情况下它等于 5 mu）

```latex
\begin{align*}
3ax+4by=5cz\\
3ax<4by+5cz
\end{align*}
```

[在 Overleaf 中打开此示例](https://www.overleaf.com/docs?engine=pdflatex\&snip_name=Math+mode+operator+spacing+example\&snip=%5Cdocumentclass%7Barticle%7D%0A%5Cusepackage%7Bamsmath%7D%0A%5Cbegin%7Bdocument%7D%0A%5Cbegin%7Balign%2A%7D%0A3ax%2B4by%3D5cz%5C%5C%0A3ax%3C4by%2B5cz%0A%5Cend%7Balign%2A%7D%0A%5Cend%7Bdocument%7D)

此示例生成如下输出：

![LaTeX 中的运算符间距](/files/4adab6c75a4a85c33954d5d832a08dd6b12e0f6e)

对于关系运算符，例如 $$<$$, $$>$$ 和 $$=$$，LaTeX 会设置 `\thickmuskip` 空格。但对于诸如 $$+$$, $$-$$ 和 $$\times$$， `\medmuskip` 之类的二元运算符，会设置空格。差别几乎难以察觉。

## 用户自定义的二元和关系运算符

你可以强制设置二元或关系运算符所使用的间距，因此你可以 [定义你自己的](/latex/zh-cn/ming-ling/01-commands.md).

```latex
\begin{align*}
34x^2a \mathbin{\#} 13bc \\
34x^2a \mathrel{\#} 13bc
\end{align*}
```

[在 Overleaf 中打开此示例](https://www.overleaf.com/docs?engine=pdflatex\&snip_name=Defining+your+own+math+operators\&snip=%5Cdocumentclass%7Barticle%7D%0A%5Cusepackage%7Bamsmath%7D%0A%5Cbegin%7Bdocument%7D%0A%5Cbegin%7Balign%2A%7D%0A34x%5E2a+%5Cmathbin%7B%5C%23%7D+13bc+%5C%5C%0A34x%5E2a+%5Cmathrel%7B%5C%23%7D+13bc%0A%5Cend%7Balign%2A%7D%0A%5Cend%7Bdocument%7D)

此示例生成如下输出：

![定义你自己的二元或关系运算符](/files/df2accde802c65f70c7c309493bb3fdc6af9e314)

前面的示例在……前后设置了特定的间距 `#` 通过使用 `\mathrel` （关系运算符）和 `\mathbin` （二元运算符）命令。

## 参考指南

**间距命令说明**

| LaTeX 代码        | 说明                                                                    |
| --------------- | --------------------------------------------------------------------- |
| `\quad`         | 空格等于当前字体大小（= 18 [mu](/latex/zh-cn/ge-shi-hua/01-lengths-in-latex.md)) |
| `\,`            | 当前字体大小的 3/18 `\quad` （= 3 mu）                                         |
| `\:`            | 当前字体大小的 4/18 `\quad` （= 4 mu）                                         |
| `\;`            | 当前字体大小的 5/18 `\quad` （= 5 mu）                                         |
| `\!`            | 当前字体大小的 -3/18 `\quad` （= -3 mu）                                       |
| `\` （反斜杠后面的空格！） | 相当于普通文本中的空格                                                           |
| `\qquad`        | 两倍于 `\quad` （= 36 mu）                                                 |

## 进一步阅读

更多信息请参见

* [数学表达式](/latex/zh-cn/shu-xue/01-mathematical-expressions.md)
* [方括号和圆括号](/latex/zh-cn/shu-xue/03-brackets-and-parentheses.md)
* [使用 amsmath 对齐方程](/latex/zh-cn/shu-xue/06-aligning-equations-with-amsmath.md)
* [数学模式中的显示样式](/latex/zh-cn/shu-xue/10-display-style-in-math-mode.md)
* [希腊字母和数学符号列表](/latex/zh-cn/shu-xue/11-list-of-greek-letters-and-math-symbols.md)
* [数学字体](/latex/zh-cn/shu-xue/12-mathematical-fonts.md)
* [LaTeX2ε 的不算太短的介绍](http://www.ctan.org/tex-archive/info/lshort/)


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