使用方程式时出错*

Question

我收到以下错误：

\documentclass[12pt,a4paper,english]{article} 
\usepackage{amsmath}
\begin{document}
\begin{equation*}
\left\{\begin{matrix}
u_t+vu_x=0 & x \in \mathbb{R}\\ 
g(x)=u(x,0)=\textrm{exp}(-10x^2) & x \in \mathbb{R}
\end{matrix}\right
\end{equation*}
\end{document}

我得到了错误

 Blockquote Missing delimiter (. inserted).
<to be read again> 
                   $
l.12 \end{equation*}                  
I was expecting to see something like `(' or `\{' or
`\}' here. If you typed, e.g., `{' instead of `\{', you
should probably delete the `{' by typing `1' now, so that
braces don't get unbalanced. Otherwise just proceed.
Acceptable delimiters are characters whose \delcode is
nonnegative, or you can use `\delimiter <delimiter code>'.

有什么问题？我不明白它为什么抱怨\end{equation*}。

Answer 1

\right.使用（其中.表示“空分隔符”）可以解决该问题。但您应该使用cases。

\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}

\begin{document}

\begin{equation*}
\left\{\begin{matrix}
u_t+vu_x=0 & x \in \mathbb{R}\\
g(x)=u(x,0)=\textrm{exp}(-10x^2) & x \in \mathbb{R}
\end{matrix}\right.
\end{equation*}

\begin{equation*}
\begin{cases}
u_t+vu_x=0               & x \in \mathbb{R}\\
g(x)=u(x,0)=\exp(-10x^2) & x \in \mathbb{R}
\end{cases}
\end{equation*}

\end{document}

并且它不是\textrm{exp}，而是\exp（这是预定义的）。请参阅\mathrm 和 \operatorname 之间有什么区别？了解更多信息。