为什么 \fillbetween two curves 命令不能部分起作用？

Question

我使用来\fillbetween填充下面显示的两条曲线之间。

它在负 x 轴上的曲线之间填充得非常奇怪。有人知道为什么吗？

这是我使用的代码

\documentclass{standalone}

\usepackage{pgfplots}
\usepackage{pgfplotstable}%fitting functions
\usepackage{tikz}
\usetikzlibrary{tikzmark}
\usepackage{pgfplotstable}
\usepgfplotslibrary{fillbetween}

\pgfkeys{/pgf/number format/.cd,1000 sep={}}


\newcommand{\myfont}{\fontfamily{cmss}\selectfont}% used with mathpazo 

\pgfplotsset{compat=1.15}
\pgfplotsset{label style={font=\normalsize},
            tick label style={font=\normalsize}}

\begin{document}

\begin{tikzpicture}
\begin{axis}[
    axis x line=bottom,
    axis y line=middle,
    enable tick line clipping=false,
    axis line style=semithick,
    width=9cm,
    height=9cm,
    x tick style={black,semithick},
    x label style=
        {at={(current axis.right of origin)},anchor=west},
    xlabel={$x$},
    xmin=-20,xmax=20,
    xtick={-15,-10,...,15},
    xtick pos=bottom,
    y tick style={black,semithick},
    y label style=
        {at={(current axis.above origin)},anchor=south},
    ylabel={$y$},
    ymin=0,ymax=40,
    ytick={-10,0,10,...,30},    
]
    \addplot [blue,very thick,name path=A] table{
    x       y
    8       0
    9.5     8
    13.5    28
    13.5    37
};

    \addplot [blue,very thick,name path=B] table{
    x   y
    10  0
    10  8
    14  28
    14  37
};

    \addplot [blue!20] fill between [of=A and B];

    \addplot [blue,very thick,name path=A1] table{
    x       y
    -10     0
    -10     8
    -14     28
    -14     37
};

    \addplot [blue,very thick,name path=B1] table{
    x       y
    -8      0
    -9.5    8
    -13.5   28
    -13.5   37
};

    \addplot [blue!20] fill between [of=A1 and B1];

    \draw [red,thick,dashed] (-20,28) -- (20,28);

    \draw [red,thick,dashed] (-20,8) -- (20,8);

\end{axis}
\end{tikzpicture}
\end{document}

Answer 1

“有人知道为什么吗？”这个问题的答案是“是的”。为了填充得不那么尴尬，你需要reverse=true填充左边的区域。为什么？因为手册在第 439 页上说

如果 pgfplots 选择了错误的，则需要手动撤销。

\documentclass{standalone}

\usepackage{pgfplots}
\usepackage{pgfplotstable}%fitting functions
\usepackage{tikz}
\usetikzlibrary{tikzmark}
\usepackage{pgfplotstable}
\usepgfplotslibrary{fillbetween}

\pgfkeys{/pgf/number format/.cd,1000 sep={}}


\newcommand{\myfont}{\fontfamily{cmss}\selectfont}% used with mathpazo 

\pgfplotsset{compat=1.15}
\pgfplotsset{label style={font=\normalsize},
            tick label style={font=\normalsize}}

\begin{document}

\begin{tikzpicture}
\begin{axis}[
    axis x line=bottom,
    axis y line=middle,
    enable tick line clipping=false,
    axis line style=semithick,
    width=9cm,
    height=9cm,
    x tick style={black,semithick},
    x label style=
        {at={(current axis.right of origin)},anchor=west},
    xlabel={$x$},
    xmin=-20,xmax=20,
    xtick={-15,-10,...,15},
    xtick pos=bottom,
    y tick style={black,semithick},
    y label style=
        {at={(current axis.above origin)},anchor=south},
    ylabel={$y$},
    ymin=0,ymax=40,
    ytick={-10,0,10,...,30},    
]
    \addplot [blue,very thick,name path=A] table{
    x       y
    8       0
    9.5     8
    13.5    28
    13.5    37
};

    \addplot [blue,very thick,name path=B] table{
    x   y
    10  0
    10  8
    14  28
    14  37
};

    \addplot [blue!20] fill between [of=A and B];

    \addplot [blue,very thick,name path=C] table{
    x       y
    -10     0
    -10     8
    -14     28
    -14     37
};

    \addplot [blue,very thick,name path=D] table{
    x       y
    -8      0
    -9.5    8
    -13.5   28
    -13.5   37
};

    \addplot [blue!20] fill between [of=D and C,reverse=true];

    \draw [red,thick,dashed] (-20,28) -- (20,28);

    \draw [red,thick,dashed] (-20,8) -- (20,8);

\end{axis}
\end{tikzpicture}
\end{document}