pgfplots 中的平方根没有被绘制

Question

我正在运行以下代码，我已经用它绘制了几个函数，但是当我用以下函数运行它时，它只绘制轴

\usepackage{pgfplots}
\usepackage{tikz}
\usetikzlibrary{decorations.markings}
\usetikzlibrary{patterns,positioning,calc}


\begin{figure}[H]

    \begin{center}

        \begin{tikzpicture}

        \begin{axis}[
        y=1cm,
        x=1cm,
        axis x line=center,
        axis y line=center,
        xtick={-1,0,...,12},
        ytick={-1,0,...,5},
        xlabel={$X$},
        ylabel={$Y$},
        xlabel style={below right},
        ylabel style={above left},
        xmin=-1,
        xmax=12.5,
        ymin=-1,
        ymax=5.5]
        \addplot+[color=black,smooth] {sqrt(x-6)};
        \end{axis}
        \end{tikzpicture}

        \caption{The graph of $f(x) = \sqrt{x-6}$} 

    \end{center}

\end{figure}

Answer 1

欢迎！只要您不尝试计算负数的平方根，一切都没问题。

\documentclass[tikz,border=3.14mm]{standalone}
\usepackage{tikz,pgfplots}
\pgfplotsset{compat=1.16}
\begin{document}

\begin{tikzpicture}

  \begin{axis}[
    y=1cm,
    x=1cm,
    axis x line=center,
    axis y line=center,
    xtick={-1,0,...,12},
    ytick={-1,0,...,5},
    xlabel={$X$},
    ylabel={$Y$},
    xlabel style={below right},
    ylabel style={above left},
    xmin=-1,
    xmax=12.5,
    ymin=-1,
    ymax=5.5]
    \addplot+[color=black,smooth,domain=6:12.5] {sqrt(x-6)};
    \end{axis}
\end{tikzpicture}
\end{document}