两条线通过同一点时，在 x=0.3 处有一个间隙。如何消除间隙？非常感谢！

Question

代码

\documentclass[border=3mm]{standalone} 
\usepackage{pgfplots}
\usepackage{tikz}
\pgfplotsset{width=10cm,compat=newest}
\usepgfplotslibrary{fillbetween}

\begin{document}
    \begin{tikzpicture}[
        declare function = {
            func1(\x)= (\x<=0.3) * (10*\x*\x - 3*\x ) + (\x>0.3) * (\x* \x*\x);
            func2(\x)= (\x<=0.3) * (0) + (\x>0.3) * (\x* \x*\x);
        }
    ]
        
        \begin{axis}[
            ymin=-0.4,
            ymax=1,
            xmin=0,
            xmax=1,
            ytick={-0.4, -0.2, 0, 0.2, 0.4, 0.6, 0.8, 1},
            grid
        ]

            \addplot[name path=poly, blue, domain=-0.4:1, smooth]{func1(x)};
            \addplot[name path=poly2, blue, domain=-0.4:1, smooth]{func2(x)};
            \addplot[name path=linear, black, no markers]{x};
            \addplot[name path=line, black, no markers]{0};
            \addplot fill between[
                of = poly and line, split,
                every odd segment/.style={red!10},
                every even segment/.style={yellow!10}
            ];
            \addplot[blue!10] fill between[of = poly2 and linear];
            \node at (axis cs:0.18,-0.05) [anchor=north east] {A};
            \node at (axis cs:0.45,0.2) [anchor=south west] {B};
            \node at (axis cs:0.8,0.3) [anchor=south west] {C};
        \end{axis}
    \end{tikzpicture} 
\end{document}

Answer 1

这是因为 x=0.3 附近的硬弯曲和smooth选项以及函数求值的样本量“较低”。您可以通过向“func”图添加标记来显示这一点，如下例所示。为了解决您的问题，您可以简单地增加samples函数求值的数量，例如增加到 101。（默认数量samples为 25。）

% used PGFPlots v1.17
\documentclass[border=3mm]{standalone}
\usepackage{pgfplots}
    \usepgfplotslibrary{fillbetween}
    \pgfplotsset{
        compat=newest,
        width=10cm,
    }
\begin{document}
    \begin{tikzpicture}[
        declare function = {
            func1(\x)= (\x<=0.3) * (10*\x*\x - 3*\x ) + (\x>0.3) * (\x* \x*\x);
            func2(\x)= (\x<=0.3) * (0) + (\x>0.3) * (\x* \x*\x);
        },
    ]
        \begin{axis}[
            ymin=-0.4,
            ymax=1,
            xmin=0,
            xmax=1,
            ytick={-0.4, -0.2, 0, 0.2, 0.4, 0.6, 0.8, 1},
            grid,
            domain=-0.4:1,
%            samples=101,   % <-- uncomment me to improve the result
        ]

            \addplot [name path=linear,black] {x};
            \addplot [name path=line,black] {0};
            \addplot [
                name path=poly,
                blue,
                smooth,
                mark=o,
            ] {func1(x)};
            \addplot [
                name path=poly2,
                red,
                smooth,
                mark=+,
            ] {func2(x)};

            \addplot fill between[
                of=poly and line,
                split,
                every odd segment/.style={red!10},
                every even segment/.style={yellow!10}
            ];

            \addplot [blue!10] fill between [of = poly2 and linear];

            \node at (axis cs:0.18,-0.05) [anchor=north east] {A};
            \node at (axis cs:0.45,0.2)   [anchor=south west] {B};
            \node at (axis cs:0.8,0.3)    [anchor=south west] {C};
        \end{axis}
    \end{tikzpicture}
\end{document}