pgflplots 中的补丁由函数分隔

Question

我有以下代码，它使我在轴上形成抛物线，我想填充抛物线下方的区域（保持在轴上）。似乎使用 plot 和 patch 应该可以实现，但我没有找到解决方案。你能帮帮我吗？

代码：

\documentclass{amsart}
\usepackage{pgf,tikz}
\usepackage{pgfplots}

\tikzset{My Line Style/.style={smooth, thick, samples=400}}


\begin{document}
\begin{center}\begin{tikzpicture}[scale=0.60]
\begin{axis}[axis lines=middle, xmin=-3.5, xmax = 3.5, ymin=-5.1, ymax = 3,xtick={-3,-2,...,3},
  ytick={-5,...,3}]
    \addplot[My Line Style, color=lightgray,  variable=\t, domain=-3.5:3.5]({\t},{\t^2-0.5});
\end{axis}
\end{tikzpicture}\end{center}\end{document}

结果应如下所示：

Answer 1

以下是实现此目的的一种可能方法。有关更多详细信息，请查看代码中的注释。

\documentclass[border=5pt]{standalone}
\usepackage{pgfplots}
    \pgfplotsset{
        % use this `compat' level or higher to use `axis cs:' coordinates by
        % default for tikz commands
        compat=1.11,
        My Line Style/.style={
            smooth,
            thick,
            samples=400,
        },
    }
\begin{document}
\begin{tikzpicture}
    \begin{axis}[
        axis lines=middle,
        xmin=-3.5,
        xmax=3.5,
        ymin=-5.1,
        ymax=3,
        xtick={-3,-2,...,3},
        ytick={-5,...,3},
        % use this so the axis is drawn on top of the everything
        axis on top,
    ]
        % first draw the fill stuff
        \addplot [
            My Line Style,
            draw=none,
            fill=lightgray!25,
            domain=-3.5:3.5,
            % restrict the y values to the maximum y axis value
            restrict y to domain*=-5.1:3,
        ] {x^2-0.5}
            % continue the path to close it
            |- (\pgfkeysvalueof{/pgfplots/xmin},\pgfkeysvalueof{/pgfplots/ymin})
        ;
        % and on top of that the line
        \addplot [
            My Line Style,
            draw=lightgray,
            domain=-3.5:3.5,
        ] {x^2-0.5}
        ;
    \end{axis}
\end{tikzpicture}
\end{document}