未使用 pgfplots 绘制的线

Question

y = 6x - 9为什么没有绘制线条？我有正确的xmin、xmax、ymin和ymax值。

\documentclass[10pt]{amsart}

\usepackage{tikz}
\usetikzlibrary{calc,intersections,}

\usepackage{pgfplots}
\pgfplotsset{compat=1.11}


\usepackage{mathtools,array}

\begin{document}


\begin{tikzpicture}
\begin{axis}[width=2.25in, height=2.75in, axis on top,
    axis lines=middle,
    xmin=-4,xmax=4, domain=-4:4,
    ymin=-4,ymax=16,
    restrict y to domain=-4:16,
    xtick={\empty}, ytick={\empty},
    xlabel=$x$,ylabel=$y$,
    axis line style={latex-latex},
    axis line style={shorten >=-12.5pt, shorten <=-12.5pt},
    xlabel style={at={(ticklabel* cs:1)}, xshift=12.5pt, anchor=north west},
    ylabel style={at={(ticklabel* cs:1)}, yshift=12.5pt, anchor=south west}
]

\addplot[samples=501, domain=-4:4] {x^2};

%\addplot[samples=2, latex-latex, domain={5/6+0.01}:{4-0.01}] {6*x - 9};
\addplot[samples=2, latex-latex, domain={5/6}:4] {6*x - 9};

\end{axis}

\end{tikzpicture}

\end{document}

Answer 1

增加点数，一切就好。

\documentclass[10pt]{amsart}

\usepackage{tikz}
\usetikzlibrary{calc,intersections,}

\usepackage{pgfplots}
\pgfplotsset{compat=1.11}


\usepackage{mathtools,array}

\begin{document}


\begin{tikzpicture}
\begin{axis}[width=2.25in, height=2.75in, axis on top,
    axis lines=middle,
    xmin=-4,xmax=4, domain=-4:4,
    ymin=-4,ymax=16,
    restrict y to domain=-4:16,
    xtick={\empty}, ytick={\empty},
    xlabel=$x$,ylabel=$y$,
    axis line style={latex-latex},
    axis line style={shorten >=-12.5pt, shorten <=-12.5pt},
    xlabel style={at={(ticklabel* cs:1)}, xshift=12.5pt, anchor=north west},
    ylabel style={at={(ticklabel* cs:1)}, yshift=12.5pt, anchor=south west}
]

\addplot[samples=501, domain=-4:4] {x^2};

%\addplot[samples=2, latex-latex, domain={5/6+0.01}:{4-0.01}] {6*x - 9};
\addplot[samples=100, latex-latex, domain={5/6}:4] {6*x - 9};

\end{axis}

\end{tikzpicture}

\end{document}