如何在轴环境中正确定义垂直线？

Question

我想要从上到下有三条垂直虚线来明显划分 4 个功能。我该怎么做？

    \documentclass[letter,12pt,twoside]{article}
\usepackage{tikz}
\usepackage{pgfplots}
\begin{document}

\begin{tikzpicture}
\begin{axis}[
    axis lines = left,
    xlabel = $\beta$,
    ylabel = {$E[\pi_B(\beta)]/10^4$},
]
\addplot [
    domain=1875/497:4, 
    samples=100, 
    color=red    
]
{5*(-(1/3) + 5/x)};

\draw[fill] (3.2,4.5) circle (2pt) coordinate (a);

\addplot [
    domain=2500/741:1875/497, 
    samples=100, 
    color=red    
]
{ 50/3 / x};

\addplot [
    domain=625/196:2500/741, 
    samples=100, 
    color=red  
]
{ 5*(1/5 + 5/2/x)};

\addplot [
    domain=305/97:625/196, 
    samples=100, 
    color=red
]
{ 5*(1/3 + 2/x)};

\end{axis}
\draw[dotted] (1875/497, 4.4) -- (1875/497,5);
\end{tikzpicture}       
\end{document}

先感谢您

Answer 1

很难说什么是“最佳”的方法，但这是一种可能的方法。

\documentclass[border=3.14mm,standalone]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.16}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
    axis lines = left,
    xlabel = $\beta$,
    ylabel = {$\alpha$},
]
\addplot [
    domain=1875/497:4, 
    samples=100, 
    color=red    
]
{5*(-(1/3) + 5/x)} coordinate[pos=0] (x1);

\addplot [
    domain=2500/741:1875/497, 
    samples=100, 
    color=red    
]
{ 50/3 / x} coordinate[pos=1] (x2);

\draw[dotted] (x1) -- (x2);

\end{axis}
\end{tikzpicture}
\end{document}

Answer 2

一种解决方案是使用格式为 (axis cs: x,y) 的坐标。这是通用的，您可以在任何地方选择任意两个点。以下是中间一行的代码。您可以用同样的方式添加其他行。

\documentclass[border=3.14mm,standalone]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.16}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
    axis lines = left,
    xlabel = $\beta$,
    ylabel = {$\alpha$},
]
\addplot [
    domain=1875/497:4, 
    samples=100, 
    color=red    
]
{5*(-(1/3) + 5/x)} ;

\addplot [
    domain=2500/741:1875/497, 
    samples=100, 
    color=red    
]
{ 50/3 / x} ;
\draw[dotted] (axis cs:3.77,0) -- (axis cs:3.77,4.95);



\end{axis}
\end{tikzpicture}
\end{document}