amsmath 已加载，但“\end{aligned}”是未定义的控制序列

Question

以下是 MWE（使用 overleaf 上的 XeLateX）：

\documentclass[11pt, a4paper, preprint]{article}
\usepackage{amsmath, amssymb, graphicx, outline, float, cite, color}
\usepackage{longtable,array}
\renewcommand{\thefigure}{S\arabic{figure}}
\renewcommand{\thetable}{S\arabic{table}}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{authblk}
\usepackage{placeins}
\usepackage{caption}
\captionsetup[figure]{font=footnotesize,labelfont=normalsize}
\usepackage{xr-hyper}
\usepackage{hyperref}
\usepackage{framed}
\usepackage{graphicx}
\graphicspath{ {Figs/} }
\newcommand{\tcr} { \textcolor{red} }

\title{compile errors}
\begin{document}

\begin{align}
    \bm{K} &= \sigma_0\\
    \text{foo} &= \text{bar}
\end{align}

\end{document}

以下是完整的错误输出：

<argument>  \bm 
                {K}(\bm {x},\bm {x'}) &= \sigma _0 + \sigma _i^2 exp 
\left [...
l.383 \end{align}

The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.

Answer 1

您没有显示错误消息：

! Undefined control sequence.
<argument>  \bm 
                {K} &= \sigma _0\\ \text {foo} &= \text {bar} 
l.25 \end{align}

? 

所以这向你表明\bm​​你需要加载未定义的命令bm。