如何制作如图所示的锯齿形箭头和线条

Question

如何制作像图片一样的锯齿形箭头和线条（描述序列收敛。

Answer 1

类似这样的事？

\documentclass[border=1cm]{standalone}
\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{calc} 
\usetikzlibrary{decorations.markings} 
% from https://tex.stackexchange.com/questions/3161/tikz-how-to-draw-an-arrow-in-the-middle-of-the-line
\begin{document}
\begin{tikzpicture}    
\begin{scope}[very thick,decoration={
    markings,
    mark=at position 0.5 with {\arrow{>}}}
    ] 
      \foreach \x in {1,2,...,8} 
       {\pgfmathsetmacro{\myx}{3*pow(-1,\x)/pow(\x,2/3)}
        \pgfmathsetmacro{\myy}{3*pow(-1,\x+1)/pow(\x+1,2/3)} 
        \pgfmathsetmacro{\myz}{\myx+0.6*pow(-1,\x)} 
        \pgfmathsetmacro{\myk}{\x-2} 
  \draw[postaction={decorate}] (\myx,\x) -- (\myy,\x+1);
  \draw[black, fill=black] (\myx,\x) circle(2pt);
  \node at (\myz,\x) {$u^{k+\x}$};}
\end{scope}
\end{tikzpicture}
\end{document}

\myx请添加和的定义系列\myy。

Answer 2

起点：

\documentclass[tikz]{standalone}
\usetikzlibrary{arrows.meta}
\begin{document}
\begin{tikzpicture}[
  >={Triangle[length=2mm, width=2.5mm]},
]
  % Coordinates
  \path
    (0, 0) coordinate (a)
    (2, 1.5) coordinate (b)
    (0, 3) coordinate (c)
    % ...
  ;

  % Points
  \fill[radius=1mm]
    \foreach \p in {a, ..., c} {
      (\p) circle[]
    }
  ;

  % Lines and middle points
  \draw
    (a) -- coordinate (ab)
    (b) -- coordinate (bc)
    (c)
  ;

  % Arrows
  \draw[->] (a) -- (ab);
  \draw[->] (b) -- (bc);

  % Labels
  \path[inner sep=.3333em + 1mm]% Added: radius of the points
    (a) node[left] {$u^{k-1}$}
    (b) node[right] {$u^{k}$}
    (c) node[left] {$u^{k + 1}$}
  ;
  \path
    (a)
    -- node[below right] {$s^{k-1}$}
    (b)
    -- node[above right] {$s^{k}$}
    (c)
  ;
\end{tikzpicture}
\end{document}