尝试画一条曲线

Question

我需要一些帮助。我是 Tikz 的初学者，我想绘制这条曲线，但我的问题是我没有曲线函数。请帮帮我！

我的 MWE 是：

\documentclass[a4paper,12pt]{article}
\usepackage[french]{babel}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{mathrsfs}
\usepackage{graphicx}
\usepackage{float}
\usepackage{pgf,tikz,pgfplots}
\begin{document}
\begin{figure}[H]
\begin{tikzpicture}[>=latex,scale=3]
\draw[->](-0.15,0)--(1.18,0);
\draw[->](0,-0.15)--(0,1.38);
\draw[color=black,samples=100, thick,domain=0:1] plot(\x,{\x});
\end{tikzpicture}
\end{figure}
\end{document}

Answer 1

欢迎！我会使用pgfplotswithgroupplots来实现这一点。在我看来，该函数看起来就像一条抛物线。您可以声明函数并以各种变体绘制它们。

\documentclass[tikz,border=3mm]{standalone}
\usepackage{pgfplots}
\usepgfplotslibrary{groupplots}
\pgfplotsset{compat=1.16}
\begin{document}
\begin{tikzpicture}[declare function={fleft(\x)=2.5-0.5*(2-\x)*(2-\x);
    fright(\x)=\x;}]
   \begin{groupplot}[group style={group size=2 by 1,horizontal sep=3em},
       width=7cm,height=6cm,
       xmin=0,xmax=4,ymin=0,
       xtick={0,1,...,4},ytick={0,1,...,4},axis lines=middle,
       xlabel={},samples=51]
    \nextgroupplot[domain=1:4,ymax=2.8,
        legend style={at={(0.05,0.1)},anchor=south west}]
      \addplot[smooth,dashed,blue] {fleft(x)+0.2};
      \addplot[smooth,dashed,blue] {fleft(x)-0.2};
      \addplot[smooth,thick] {fleft(x)};
      \addplot[smooth,red,thick,samples=101] {fleft(x)+0.1*sin(x*540)};
      \legend{$f+\varepsilon$,$f-\varepsilon$,$f$,$f_N$}
    \nextgroupplot[domain=0:4,legend style={at={(0.05,0.95)},anchor=north west}]
      \addplot[smooth,dashed,blue] {fright(x)+0.2};
      \addplot[smooth,dashed,blue] {fright(x)-0.2};
      \addplot[smooth,thick] {fright(x)};
      \addplot[smooth,red,thick,samples=101] {fright(x)+0.1*sin(x*540)};
      \legend{$f+\varepsilon$,$f-\varepsilon$,$f$,$f_{10}$}
   \end{groupplot}
\end{tikzpicture}
\end{document}