> For the complete documentation index, see [llms.txt](https://overleaf-pro.ayaka.space/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://overleaf-pro.ayaka.space/latex/zh-cn/latex-cuo-wu/06-extra-right.md).

# 多余的 \right

当排版数学公式时，如果使用了 \right 命令但缺少对应的 \left，就会发生此错误。本文讨论了该错误的常见原因以及如何修复。

## \left 和 \right 命令简介

该 `\left` 和 `\right` 这些命令用于排版动态大小的定界符，必须在数学内容中配合使用，形式为

$$\verb'\left'\thinspace\textit{delim}*{\thinspace\text{L}}\quad\textit{math expression}\quad \verb'\right'\thinspace\textit{delim}*{\thinspace\text{R}}$$

其中 $$\textit{delim}*{\thinspace\text{L}}$$ 和 $$\textit{delim}*{\thinspace\text{R}}$$ 是用于包围你的……的定界符 $$\textit{math expression}$$通常， $$\textit{delim}*{\thinspace\text{L}}$$ 和 $$\textit{delim}*{\thinspace\text{R}}$$ 是以下字符之一 `() [] | \| \{ \}` 或句点 “`.`”，它用作“[空白定界符](#using-a-blank-delimiter)”。

### 示例

这里有一个使用 `\left` 和 `\right` 用于排版完全包围分数的圆括号：

```latex
\[
  \left(\frac{x}{y} \right)
\]
```

此代码生成 $$\left(\frac{x}{y}\right)$$

如果你不使用 `\left` 和 `\right` 在放置定界符（包括圆括号）时使用这些命令，这些定界符将不会完全包围数学表达式；例如，写作

```latex
\[
  (\frac{x}{y})
\]
```

会生成这个

$$(\frac{x}{y})$$

## 此错误的原因及一些解决方法

### 忘记包含 \left 命令

此错误通常在编写一个 `\right` 命令时出现，但忘记包含相应的 `\left`，如下例所示：

```latex
\[
\pi =
( \int_{-\infty}^{+\infty} e^{-x^2} dx \right)
\]
```

[在 Overleaf 中打开此 **会产生错误的** Overleaf 中的示例](https://www.overleaf.com/docs?engine=pdflatex\&snip_name=Example+demonstrating+a+missing+delimiter\&snip=%5Cdocumentclass%7Barticle%7D%0A%5Cbegin%7Bdocument%7D%0A%5C%5B+%0A%5Cpi+%3D+%0A%28+%5Cint_%7B-%5Cinfty%7D%5E%7B%2B%5Cinfty%7D+e%5E%7B-x%5E2%7D+dx+%5Cright%29%0A%5C%5D%0A%5Cend%7Bdocument%7D)

此示例会生成以下错误：

![用于演示 LaTeX 中缺少定界符的图片](/files/4f2f4f6321b0bee07c8c30d7f6078080f304ee07)

添加缺少的 `\left` ，通过编写以下内容来修复此错误

```latex
\[
\pi =
\left( \int_{-\infty}^{+\infty} e^{-x^2} dx \right)
\]
```

，其会生成以下输出

$$\pi = \left( \int\_{-\infty}^{+\infty} e^{-x^2} dx \right)$$

### 使用空定界符

如果你想排版一个 `\right` 仅定界符，请使用 ‘`.`’ 字符作为 `\left` 定界符，方法是写 `\left.`，它不会排版出定界符字符。下面的示例使用了一个 `.` 定界符在一个 `aligned` 环境中进行程序代码排版，该环境由 `amsmath` 宏包的示例代码：

```latex
\documentclass{article}
\usepackage{amsmath} % 需要使用 aligned 环境

\begin{document}
\[
 \left.\begin{aligned}
        dF &= 0,\\
        d^{\dagger} F &= 0,
       \end{aligned}
\ \right\}
 \qquad \text{麦克斯韦方程组}
\]
\end{document}
```

[在 Overleaf 中打开此示例](https://www.overleaf.com/docs?engine=pdflatex\&snip_name=Using+the+dot+delimiter\&snip=%5Cdocumentclass%7Barticle%7D%0A%5Cusepackage%7Bamsmath%7D+%25+Required+to+use+the+aligned+environment%0A%0A%5Cbegin%7Bdocument%7D%0A%5C%5B%0A+%5Cleft.%5Cbegin%7Baligned%7D%0A++++++++dF+%26%3D+0%2C%5C%5C%0A++++++++d%5E%7B%5Cdagger%7D+F+%26%3D+0%2C%0A+++++++%5Cend%7Baligned%7D%0A%5C+%5Cright%5C%7D%0A+%5Cqquad+%5Ctext%7BMaxwell%27s+equations%7D%0A%5C%5D%0A%5Cend%7Bdocument%7D)

此示例会排版出以下表达式：

$$\left.\begin{aligned} dF &= 0,\d^{\dagger} F &= 0,\end{aligned}\ \right}\qquad \text{Maxwell's equations}$$


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