描述 X 轴上的交点

Question

我有两个函数在三个不同的点相交：

\documentclass{article}

\usepackage{tikz}
\usepackage{tkz-euclide}
\usetikzlibrary{intersections}
\usepackage{pgfplots}

\begin{document}

\begin{tikzpicture}
\begin{axis}[
axis x line=bottom, axis y line=left,
width=12cm, height=8cm,
xlabel=$x$, ylabel=$y$,
ticks=none
]
\addplot[color=blue, line width=1pt, name path global=identity]{x};
\addplot[red, line width=1pt, name path global=function] {12/(1.5+e^(-x))-4};
\path [draw,name intersections={of={function and identity}}]
  (intersection-1) circle[radius=2pt]
  (intersection-2) circle[radius=2pt]
  (intersection-3) circle[radius=2pt];
\end{axis}
\end{tikzpicture}

\end{document}

我想通过从交点到垂直于 y 轴的 X 轴绘制一条线来描述交点。例如

但我不确定如何在绘制线条时管理交叉点坐标......

Answer 1

如果O是轴的原点，您可以使用来获取在Ox轴上(A|-O)的投影，并获取在Oy轴上的投影。A(A-|O)

\documentclass[tikz,border=50]{standalone}
%\usepackage{tkz-euclide}
\usetikzlibrary{intersections}
\usepackage{pgfplots}
\tikzset{
  point/.style={insert path={node[circle, inner sep=1.5pt, fill]{}}}
}
\begin{document}
  \begin{tikzpicture}
    \begin{axis}[
        axis x line=bottom, axis y line=left,
        width=12cm, height=8cm,
        xlabel=$x$, ylabel=$y$,
        ticks=none
      ]
      \addplot[color=blue, line width=1pt, name path global=identity]{x};
      \addplot[red, line width=1pt, name path global=function] {12/(1.5+e^(-x))-4};
      \path [draw,name intersections={of=function and identity, by={A,B,C}}];
    \end{axis}
    \coordinate (O); % set (O)=(0,0)
    \foreach \p/\l in {A/Lable1,B/Label2,C/Label3}
      \path[draw=red, dashed] (\p) [point] -- (\p|-O) node[point,below]{\l};
  \end{tikzpicture}
\end{document}