如何使用 TikZ 或 PGF 绘制以下图片？

Question

如何使用 TikZ 或 PGF 绘制以下图片？

Answer 1

看看你是否能学到一些东西，例如下面这个：

\documentclass[tikz, border=3mm]{standalone}

\begin{document}
    \begin{tikzpicture}
\draw[->]   (0,0) -- + (77mm,0) node[below left] {$t$};
\draw[->]   (0,3) -- + (77mm,0) node[below left] {$t$};
\draw[->]   (1,-0.1) -- + (0,66mm) node[below left] {$u$};
%
\draw (6,3.1) -- + (0,-0.2) node[below] {$t_{\max}$};
\draw (6,0.1) -- + (0,-0.2) node[below] {$t_{\max}$};
%
\draw[blue,very thick] (1,5) node[left] {$u_1$} -| (3,3) node[below] {$t_1$};
%
\draw[blue,very thick] (1,2) node[left] {$u_2$} -- + (0.2,0);
\draw[blue,very thick] (3,0) |- (5,2) -- (5,0) node[below] {$t_2$};
    \end{tikzpicture}
\end{document}