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阴影问题

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阴影问题

y=-x^2, y=x^2+1我正在尝试为抛物线和线条所包围的区域进行着色x=-1, x=3。

通过在这里使用@Salim Bou 的答案pgfplots 使用多条曲线填充，我使用了以下代码：

\begin{figure}[h]
  \begin{tikzpicture}
   \begin{axis}
     [xlabel=$x$,ylabel=$y$,axis lines=middle,xtick={30},ytick={30},no marks,axis equal,xmin=-2,xmax=4,ymin=-10,ymax=10,enlargelimits={upper=0.1}]

     \addplot[no markers,thick,samples=1001, samples y=0,domain=-1:3,variable=x, name path=A]({ x },{ -x^2 });
     \addplot[no markers,thick,samples=1001, samples y=0,domain=-1:3,variable=x, name path=B]({ x },{ x^2+1 });

     \addplot[no markers,thick,samples=3, samples y=0,domain=-1:2,variable=t]({ -1 },{ t });
     \addplot[no markers,thick,samples=3, samples y=0,domain=-9:10,variable=t]({ 3 },{ t });

     \addplot[gray!30,opacity=0.6] fill between[of=A and B, soft clip={domain=-1:3}];

     \node[above right] at (0,0) {\scalebox{0.5}{$O$}};
     \node[below left] at (-1,0) {\scalebox{0.5}{$-1$}};
     \node[below right] at (3,0) {\scalebox{0.5}{$3$}};

  \end{axis}
 \end{tikzpicture}
\end{figure}

但在我的示例中该命令似乎\addplot[gray!30,opacity=0.6] fill between[of=A and B, soft clip={domain=-1:3}]没有任何效果。

我怎样才能解决这个问题 ？

在此处输入图片描述

答案1

在等待错误修复时，您可以使用pgfplots无soft clip宏：

\documentclass[margin=3mm]{standalone}
\usepackage{pgfplots}
\usepgfplotslibrary{fillbetween}
\usetikzlibrary{intersections, positioning}

\begin{document}
    \begin{tikzpicture}[node distance=0pt,
                        N/.style={font=\tiny, inner sep=1pt}
                        ]
\begin{axis}[
    axis lines=middle,
    axis equal,
    xlabel=$x$,    ylabel=$y$,
    xtick=\empty,  ytick=\empty,
    xmin=-2,  xmax=4,
    ymin=-10, ymax=10,
    no marks,
    samples=101,
    domain=-1:3
    ]
 \addplot[thick,name path=A] {-x^2};
 \addplot[thick,name path=B] { x^2+1};

 \draw[thick] (axis cs:-1,-1) -- (axis cs:-1,2);
 \draw[thick] (axis cs: 3,-9) -- (axis cs:3,10);

 \addplot[gray!30,opacity=0.6] fill between[of=A and B];

 \node[N, above right=of {axis cs: 0,0}]  {$ 0$};
 \node[N, below  left=of {axis cs:-1,0}]  {$-1$};
 \node[N, below right=of {axis cs: 3,0}]  {$ 3$};
\end{axis}
    \end{tikzpicture}
\end{document}

在此处输入图片描述

答案2

在等待错误修复的同时，以下是元帖子，你可以用它编译lualatex（或改编为普通 MP，或GMP包装）。

在此处输入图片描述

\RequirePackage{luatex85}
\documentclass[border=5mm]{standalone}
\usepackage{luamplib}
\begin{document}
\mplibtextextlabel{enable}
\begin{mplibcode}
beginfig(1);
    numeric u, s;
    u = 5mm;

    path xx, yy, pp, A, B, S;
    xx = (left--right) scaled 8u;
    yy = xx rotated 90;

    s = 1/8;
    pp = ( (-1,1) for x = s-1 step s until 3: -- (x,x**2) endfor ) scaled u;

    A = pp shifted (0,u);
    B = reverse pp reflectedabout(left, right);
    S = A -- B -- cycle;

    fill S withcolor 3/4 white;
    drawarrow xx withcolor 1/4 white;
    drawarrow yy withcolor 1/4 white;
    draw S;

    label.rt("$x$", point 1 of xx);
    label.top("$y$", point 1 of yy);

    label.llft("$-1$", (-u,0));
    label.lrt("$3$", (3u,0));

endfig;
\end{mplibcode}
\end{document}

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