PGF中的tick标记问题

使用 `tickwidth=0pt` 将 tick 的线宽调整为 0，怎么把 tick 调整成点我不太会。 直接画虚线就可以标记坐标，使用 `clip mode=individual` 避免将 $f(xi_i)$ 裁切掉。 完整代码： ``` \documentclass[border=5mm]{standalone} \usepackage{pgfplots} \pgfplotsset{compat=1.17} \usetikzlibrary{intersections} %\usepgfplotslibrary{fillbetween} \begin{document} \begin{tikzpicture}[scale=0.9, declare function={ f(\x)=2+sin(deg(\x-2))+sin(deg(3*\x))/2+sin(deg(5*\x))/8 + sin(deg(7*\x))/28; } ] \begin{axis}[ axis lines = middle, xtick ={.90,1.5,2,2.5,3,3.5,4.1}, ytick ={0}, xticklabels = {$a=x_0$,$x_1$,$\ldots$,$x_i$,$\ldots$ , $x_{n-1}$,$x_n=b$}, ymin = -0.2, ymax = 3.7, xmin = -0.2, xmax = 5.2, x=3cm,y=2cm, axis line style = thick, tickwidth=0pt, % 调整 tick 线宽 clip mode=individual, % 避免裁切 node 文字 % xlabel={$x$}, % ylabel={$y$}, extra x ticks={1.25,1.75,2.25,2.75,3.25,3.75}, extra x tick labels={$\xi_1$, $\ldots$, $\xi_i$, $\ldots$, $\xi_{n-1}$, $\xi_n$}, ] \addplot [ domain=1:4, samples=300, line width=1pt, fill=red, draw=none, fill opacity=0.1 ] {f(x)} \closedcycle; \addplot [ domain=1:4, samples=300, line width = 1pt, red] {f(x)}; \addplot [ ycomb, thick, red, no markers, samples at={1,1.5,...,4} ] {f(x)}; \addplot [ ycomb, dashed, blue, no markers, samples at={1.25,1.75,2.25,2.75,3.25,3.75} ] {f(x)}; \draw[dashed] (axis cs:2.25,{f(2.25)}) -- (axis cs:0,{f(2.25)}) node[left] {$f(\xi_i)$}; \end{axis} \end{tikzpicture} \end{document} ``` 效果：