使用 pgfplots 生成此图片

Question

我可以使用 pgfplots 生成不同颜色的抛物线，但是我无法在图表上画箭头。

\documentclass{article}
\usepackage{pgfplots}
\usetikzlibrary{arrows}

\begin{document}
\begin{tikzpicture} 
   \begin{axis}[axis lines=middle,
     xmin=-2,xmax=5,ymin=-15,ymax=15,
     xlabel=$x$,   
     ylabel={$y$},
     xtick distance=1
   ]

   \addplot[smooth,color=blue,] {x^2-x+2}; 
  \end{axis} 
\end{tikzpicture}
\end{document}

Answer 1

这是一项提议。箭头是通过 来添加的decorations.markings，而不是使用已弃用的arrows库。除其他事项外，还确保无需使用来切换到轴坐标。arrows.meta\pgfplotsset{compat=1.16}axis cs

\documentclass{article}
\usepackage{pgfplots}
\pgfplotsset{compat=1.16}
\usetikzlibrary{arrows.meta,decorations.markings}

\begin{document}
\begin{tikzpicture}[add arrow/.style 2 args={postaction=decorate,decoration={%
markings,mark=at position #1 with {\arrow{#2}}}}] 
   \begin{axis}[axis lines=middle,width=6cm,height=8cm,
     xmin=-0.5,xmax=5,ymin=0,ymax=10,domain=-0.5:4,
     xlabel=$x$,   
     ylabel={$y$},
     xtick distance=1
   ]

   \addplot[smooth,color=blue,add arrow={0.25}{Stealth[purple,length=5pt]},
   add arrow={0.36}{Stealth[reversed,purple,length=5pt]}] {x^2-x+2}; 
   \draw[yellow!70!black,dashed] (0,4) -| (2,0)
   node[pos=0.1,black,fill=white](4){4}
   node[pos=0.9,black,fill=white](2){2};
  \end{axis} 
   \draw[red,latex-] (4) edge ++ (0,0.5) edge ++ (0,-0.5)
   (2) edge ++ (0.5,0) edge ++ (-0.5,0);
\end{tikzpicture}
\end{document}