当 y 轴在左边、x 轴在底部时，怎样在原点处绘制一个完整的圆？

Question

我试图在原点处绘制一个圆形节点，同时保持 y 轴在左侧，x 轴在底部。节点结果为四分之一圆。如何在保留轴的同时保持其为整圆？

下面是我正在使用的代码。

\begin{tikzpicture}[baseline]
\begin{axis}[
    axis y line = left,
    axis x line=bottom,
    xlabel = t,
    xtick = {\empty},
    ytick =  {\empty},
]
\addplot [
    domain=-6:6, 
    samples=100, 
    color=gray,
    line width = 0.55mm,
    ]
    {1/(1+exp(-\x))};
   \draw[fill] (0,0) circle[radius=3pt];  
    \end{axis} ;

\end{tikzpicture}
}

谢谢你！

Answer 1

一种可能性是

after end axis/.code={\draw[fill] (current axis.origin) circle[radius=3pt];}

以避免节点在轴的边界处被剪裁。相反，(current axis.origin)您也可以(axis cs:0,0)在上面的代码中使用。

\documentclass[margin=5pt]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\begin{document}
\begin{tikzpicture}[baseline]
\begin{axis}[
    axis y line = left,
    axis x line=bottom,
    xlabel = t,
    xtick = {\empty},
    ytick =  {\empty},
    after end axis/.code={\draw[fill] (current axis.origin) circle[radius=3pt];}
]
\addplot [
    domain=-6:6, 
    samples=100, 
    color=gray,
    line width = 0.55mm
    ]
    {1/(1+exp(-\x))};
    \end{axis}
\end{tikzpicture}
\end{document}

Answer 2

我会用

\addplot[color=black,only marks,mark=*] (-6,0);

这使

以下是完整的 MWE：

% arara: pdflatex
\documentclass{standalone}
\usepackage{pgfplots}

\begin{document}

\begin{tikzpicture}
\begin{axis}[
    axis y line = left,
    axis x line=bottom,
    xlabel = t,
    xtick = {\empty},
    ytick =  {\empty},
]
\addplot [
    domain=-6:6, 
    samples=100, 
    color=gray,
    line width = 0.55mm,
    ]
    {1/(1+exp(-\x))};
   \addplot[color=black,only marks,mark=*] (-6,0);
    \end{axis} 

\end{tikzpicture}


\end{document}