![简单条件方程](https://linux22.com/image/477762/%E7%AE%80%E5%8D%95%E6%9D%A1%E4%BB%B6%E6%96%B9%E7%A8%8B.png)
我测试了一些解决方案,但没有得到简单的结果。美学上我想使用箭头。而不是括号。公式后面是带有条件解释的文本。你对此有什么简单的建议吗?谢谢
\documentclass[a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage[italian]{babel}
\usepackage{amsmath}
\usepackage{tikz}
\usepackage{mwe}
\usepackage{lmodern}
\makeatletter
\DeclareMathSizes{\@xpt}{\@xpt}{5}{4}
\DeclareMathSizes{\@xipt}{\@xipt}{6}{5}
\DeclareMathSizes{\@xiipt}{\@xiipt}{6}{5}
\DeclareMathSizes{\@xivpt}{\@xivpt}{\@xpt}{6}
\makeatother
\begin{document}
$
\alpha = m\frac{l'\,z}{l_{0}}\;
\begin{cases}
>0\\=0\\<0
\end{cases}
$
$
\alpha = m\frac{l'\,z}{l_{0}}
\begin{array}{c}
\nearrow >0\\
\rightarrow = 0\\
\searrow < 0\\
\end{array}
$
\end{document}
------------更新------------------
这就是我想要得到的:
\begin{center}
\begin{subequations}
\begin{minipage}{.32\textwidth}
\centering
\begin{equation}
\begin{aligned}
P_{G} = \frac{1}{\rho_{z}}gz_{,i}(\overline{\rho'u_{i}'})\label{eq097.4a}
\end{aligned}
\end{equation}
\end{minipage}\hfil
\begin{minipage}{.30 \textwidth}
%\centering
\begin{equation}
\begin{aligned}
P_{G} = \frac{1}{\rho_{z}}g(\overline{\rho' w'})\label{eq097.4b}
\end{aligned}
\end{equation}
\end{minipage}\hfill
\begin{minipage}{.35 \textwidth}
\begin{equation}
\begin{aligned}
P_{G} = g\frac{\overline{\theta' w'}}{\theta_{0}}\label{eq097.4c}\;
\begin{array}{c@{\;}l}
&>0\\[-.75ex]
\nearrow\\
\rightarrow &= 0\\
\searrow\\[-.5ex]
&< 0
\end{array}
\end{aligned}
\end{equation}
\end{minipage}%\hfill
\end{subequations}
\end{center}
答案1
答案2
答案3
这里使用两个单独的堆栈完成,以便箭头垂直间隙可以与条件堆栈的基线跳跃不同。
\documentclass[a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage[italian]{babel}
\usepackage{amsmath}
\usepackage{tikz}
\usepackage{mwe}
\usepackage{lmodern}
\makeatletter
\DeclareMathSizes{\@xpt}{\@xpt}{5}{4}
\DeclareMathSizes{\@xipt}{\@xipt}{6}{5}
\DeclareMathSizes{\@xiipt}{\@xiipt}{6}{5}
\DeclareMathSizes{\@xivpt}{\@xivpt}{\@xpt}{6}
\makeatother
\usepackage[usestackEOL]{stackengine}
\stackMath
\newcommand\arrowstack{\,\ensurestackMath{\stackengine{\Sstackgap}{%
\stackengine{\Sstackgap}{\rightarrow}{\nearrow}{O}{c}{F}{F}{S}%
}{\searrow}{U}{c}{F}{F}{S}%
}}
\begin{document}
\[
\setstackgap{L}{16pt}% GOVERNS THE CONDITIONS STACK BASELINESKIP
\setstackgap{S}{2pt}% GOVERNS THE ARROW STACK GAP
\alpha = m\frac{l'\,z}{l_{0}}
\arrowstack
\Centerstack[l]{{}>0\\{}=0\\{}<0}
\]
\end{document}