我在 TikZ/pgfplots 圖片中發現的一個錯誤

Question

這是我的程式碼：

\begin{tikzpicture} 
    [
        scale=1.05,
        declare function=
        {
            funcc(\x)=
            %(\x<-0.6) * (\x)+
            (\x<-0.6) * (0.7285067873303168+2.058823529411765*\x+2.1606334841628962*\x^2 + 0.7918552036199096*\x^3)+
            and(\x>=-0.6,\x<-0.4) * (1.1411764705882352+ 4.294117647058823*\x + 6.029411764705881*\x^2 + 
            2.941176470588235*\x^3)+
            and(\x>=-0.4,\x < -0.2) * (0.5*(2 + 6*\x + 5*\x^2))+
            and(\x>=-0.2,\x <0) * (1 +1*\x - 12.5*\x^2 - 25*\x^3)+
            and(\x>=0,\x <0.2) * (1 - 1*\x - 12.5*\x^2 +25*\x^3)+
            add(\x>=0.2,\x < 0.4) * (0.5*(2 - 6*\x + 5*\x^2))+
            and(\x>=0.4 ,\x<0.6) * (1.14118 - 4.29412*\x + 6.02941*\x^2 - 2.94118*\x^3) +
            %(\x>=0.6) * (\x^3);
            (\x>=0.6) * (0.728507 - 2.05882*\x + 2.16063*\x^2 - 0.791855*\x^3);
        },
    ]
\begin{axis}
    [
    title = {},%\quad The distribution of the points and the line of regression},
    axis lines = middle,
    legend pos=outer north east,
    xlabel={$x$},
    ylabel={$y$},
    xmin=-2, xmax=2,
    ymin=-2, ymax=2,
    ]
    \addplot%S 10
    [
    domain = -1:1,
    legend pos=outer north east,
    color=yellow,
    samples = 1000
    ]
    {
        (\x<-0.6) * (0.7285067873303168+2.058823529411765*\x+2.1606334841628962*\x^2 + 0.7918552036199096*\x^3)+
            and(\x>=-0.6,\x<-0.4) * (1.1411764705882352+ 4.294117647058823*\x + 6.029411764705881*\x^2 + 
            2.941176470588235*\x^3)+
            and(\x>=-0.4,\x < -0.2) * (0.5*(2 + 6*\x + 5*\x^2))+
            and(\x>=-0.2,\x <0) * (1 +1*\x - 12.5*\x^2 - 25*\x^3)+
            and(\x>=0,\x <0.2) * (1 - 1*\x - 12.5*\x^2 +25*\x^3)+
            add(\x>=0.2,\x < 0.4) * (0.5*(2 - 6*\x + 5*\x^2))+
            and(\x>=0.4 ,\x<0.6) * (1.14118 - 4.29412*\x + 6.02941*\x^2 - 2.94118*\x^3) +
            %(\x>=0.6) * (\x^3);
            (\x>=0.6) * (0.728507 - 2.05882*\x + 2.16063*\x^2 - 0.791855*\x^3)
    };
    
    \addplot %N 10
    [
    domain = -1:1,
    legend pos=outer north east,
    color=green,
    samples = 1000
    ]
    {
        -220.942*x^10+494.91*x^8-381.434*x^6+123.36*x^4-16.8552*x^2+1.
    };
    \addplot %N_{5}
    [
    domain = -1:1,
    legend pos=outer north east,
    color=blue,
    samples = 1000
    ]
    {
        1.20192*x^4-1.73077*x^2+0.567308
    };
    %\addlegendentry{$N_{5}(x)$}
    \addplot %f(x)
    [
    domain = -1:1,
    legend pos=outer north east,
    color=red,
    samples = 1000
    ]
    {
        1 /(1+25*x^2)
    };
    %\addlegendentry{$f(x) = \frac{1}{1+25x^{2}}$}
    \legend{$S_{10}(x)$,$N_{10}(x)$,$N_{5}(x)$,$f(x) = \frac{1}{1+25x^{2}}$};
    \end{axis}
\end{tikzpicture}   

結果如下：

黃線應該與紅線幾乎相等，但差異太大了。

我從 Mathematica 得到的黃線的正確結果如下：

無論如何，我找不到我的錯誤，所以我認為問題出在 pdgplots 本身。

Answer 1

全部add改為and：

\documentclass[border=1cm]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.18}
\begin{document}
\begin{tikzpicture} 
    [
        scale=1.05,
        declare function=
        {
            funcc(\x)=
            %(\x<-0.6) * (\x)+
            (\x<-0.6) * (0.7285067873303168+2.058823529411765*\x+2.1606334841628962*\x^2 + 0.7918552036199096*\x^3)+
            and(\x>=-0.6,\x<-0.4) * (1.1411764705882352+ 4.294117647058823*\x + 6.029411764705881*\x^2 + 
            2.941176470588235*\x^3)+
            and(\x>=-0.4,\x < -0.2) * (0.5*(2 + 6*\x + 5*\x^2))+
            and(\x>=-0.2,\x <0) * (1 +1*\x - 12.5*\x^2 - 25*\x^3)+
            and(\x>=0,\x <0.2) * (1 - 1*\x - 12.5*\x^2 +25*\x^3)+
            and(\x>=0.2,\x < 0.4) * (0.5*(2 - 6*\x + 5*\x^2))+
            and(\x>=0.4 ,\x<0.6) * (1.14118 - 4.29412*\x + 6.02941*\x^2 - 2.94118*\x^3) +
            %(\x>=0.6) * (\x^3);
            (\x>=0.6) * (0.728507 - 2.05882*\x + 2.16063*\x^2 - 0.791855*\x^3);
        },
    ]
\begin{axis}
    [
    title = {},%\quad The distribution of the points and the line of regression},
    axis lines = middle,
    legend pos=outer north east,
    xlabel={$x$},
    ylabel={$y$},
    xmin=-2, xmax=2,
    ymin=-2, ymax=2,
    ]
    \addplot%S 10
    [
    domain = -1:1,
    legend pos=outer north east,
    color=yellow,
    samples = 100
    ]
    {
        (\x<-0.6) * (0.7285067873303168+2.058823529411765*\x+2.1606334841628962*\x^2 + 0.7918552036199096*\x^3)+
            and(\x>=-0.6,\x<-0.4) * (1.1411764705882352+ 4.294117647058823*\x + 6.029411764705881*\x^2 + 
            2.941176470588235*\x^3)+
            and(\x>=-0.4,\x < -0.2) * (0.5*(2 + 6*\x + 5*\x^2))+
            and(\x>=-0.2,\x <0) * (1 +1*\x - 12.5*\x^2 - 25*\x^3)+
            and(\x>=0,\x <0.2) * (1 - 1*\x - 12.5*\x^2 +25*\x^3)+
            and(\x>=0.2,\x < 0.4) * (0.5*(2 - 6*\x + 5*\x^2))+
            and(\x>=0.4 ,\x<0.6) * (1.14118 - 4.29412*\x + 6.02941*\x^2 - 2.94118*\x^3) +
            %(\x>=0.6) * (\x^3);
            (\x>=0.6) * (0.728507 - 2.05882*\x + 2.16063*\x^2 - 0.791855*\x^3)
    };
    
    \addplot %N 10
    [
    domain = -1:1,
    legend pos=outer north east,
    color=green,
    samples = 100
    ]
    {
        -220.942*x^10+494.91*x^8-381.434*x^6+123.36*x^4-16.8552*x^2+1.
    };
    \addplot %N_{5}
    [
    domain = -1:1,
    legend pos=outer north east,
    color=blue,
    samples = 100
    ]
    {
        1.20192*x^4-1.73077*x^2+0.567308
    };
    %\addlegendentry{$N_{5}(x)$}
    \addplot %f(x)
    [
    domain = -1:1,
    legend pos=outer north east,
    color=red,
    samples = 100
    ]
    {
        1 /(1+25*x^2)
    };
    %\addlegendentry{$f(x) = \frac{1}{1+25x^{2}}$}
    \legend{$S_{10}(x)$,$N_{10}(x)$,$N_{5}(x)$,$f(x) = \frac{1}{1+25x^{2}}$};
    \end{axis}
\end{tikzpicture}   
\end{document}

黃色圖靠近​​紅色圖。顯然，我不知道你想做什麼，但看起來你犯這個錯誤的可能性比這是因為錯誤造成的。