如何在 Latex 中编写长积分

Question

请帮我解决这个问题。我想像图中那样写长积分。这是我的代码，但它在 Texmaker 中不起作用。请帮忙！非常感谢！

\begin{align}%\label{2.37}
\begin{split}
&\left\|r_{xx}\right\|^2_{L^{\infty}(0,T;L^2(\Omega))}=\sup_{t}{\int_0^1{\left(\int_0^t{\left(\frac{D_2}{\int_0^1{\bar{r}\,H_{\epsilon}(\bar{u}+g)}dx}cat_{xx}(u+g)+\right. \right.\\
&\left. \left.+2\frac{D_2}{\int_0^1{\bar{r}\,H_{\epsilon}(\bar{u}+g)}dx}cat_{x}(u_x+g_x)+\frac{D_2}{\int_0^1{\bar{r}\,H_{\epsilon}(\bar{u}+g)}dx}cat(x)(u_{xx}+g_{xx})\right)d\tau\right)^2}}dx}\leq
\end{split}
\end{align}

Answer 1

在三行中使用\MoveEqLeft和multlined环境amsmath和mathtools包（第二行也加载第一行）和窃取的数学运算符和定义区分运算符的d想法伯纳德回答：

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[showframe]{geometry}
\usepackage{mathtools}
\DeclareMathOperator{\cat}{cat}
\DeclarePairedDelimiter{\norm}{\lVert}{\rVert}
\newcommand*{\ud}{\mathrm{\,d}}     % differential symbol for integrals

\begin{document}

\begin{align}%\label{2.37}
    \MoveEqLeft
\norm{r_{xx}}^2_{L^{\infty}(0,T;L^2(\Omega))} = &     \notag    \\
  & \begin{multlined}[t][0.7\linewidth]
  \sup_{t}\int_0^1\left\lgroup\int_0^t 
    \left\lgroup\frac{D_2}{\int_0^t \bar{r}\,H_{\epsilon}(\bar{u}+g)\ud x} \cat_{xx}(u+g)+2\frac{D_2}{\int_0^1{\bar{r}\,H_{\epsilon}(\bar{u}+g)}\ud x} \cat_{x}(u_x+g_x)\right.\right.                             \\                
    \left.\left.+ \frac{D_2}{\int_0^1\bar{r}\,H_{\epsilon}(\bar{u}+g)\ud x} \cat_x(u_{xx}+g_{xx})\right\rgroup\ud\tau \right\rgroup^{2}\ud x\leq
    \end{multlined}
\end{align}

\end{document}

Answer 2

根据环境，我建议将此布局分为三行flalign。我擅自将其解释cat为某个函数的名称，因此必须用罗马字母输入，所以我通过命令将其声明为数学运算符\cat。我还定义了一个\norm命令，带有一个可自动调整其内容的带星号的版本，以及一个\dd用于积分中的微分符号的命令，具有正确的间距，以 upshape 形式输入。

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[showframe]{geometry}
\usepackage{mathtools}
\DeclareMathOperator{\cat}{cat}
 \DeclarePairedDelimiter{\norm}{\lVert}{\rVert}%
\newcommand*{\dd}{\mathop{}\!\mathrm{d}} %% differential symbol for integrals

\begin{document}

\begin{flalign}%\label{2.37}
  & \mathrlap{\norm{r_{xx}}^2_{L^{\infty}(0,T;L^2(\Omega ))}=} & & & &\notag \\
  & &\sup_{t}\int_0^1\Biggl(\int_0^t\Biggl(\frac{D_2}{\int_0^1 \bar{r}\,H_{\epsilon }(\bar{u}+g)\dd x} \cat_{xx}(u+g)+2\frac{D_2}{\int_0^1{\bar{r}\,H_{\epsilon }(\bar{u}+g)}\dd x}\cat_{x}(u_x+g_x)& \\[-1ex]
  & &{}+ \frac{D_2}{\int_0^1\bar{r}\,H_{\epsilon }(\bar{u}+g)dx} \cat(x)(u_{xx}+g_{xx})\Biggr)\!\dd\tau&\Biggr)^{\!\!2\!}\dd x\leq \notag
\end{flalign}

\end{document}