Pgfplots-绘图未达到轴：间隙与域和样本

Question

考虑下面的例子，它运行良好，但我们不太明白为什么。

如果我们改用，domain=-1:1则会得到差距：

而domain=-2:2给我们

正如我们所希望的。

同时如果我们在这种domain=-2:2情况下改用samples=1000我们得到

与第一幅图像相比，其间隙不同。

那里到底发生了什么，为什么在这种情况下domain=-2:2+会起作用？samples=1001

如果相关，则使用 TL17 冻结进行编译。

梅威瑟：

\documentclass[10pt]{standalone}
\usepackage{tikz,pgfplots}
\pgfplotsset{compat=1.15}
\usetikzlibrary{arrows.meta}

\tikzset{
  >={Latex[round]},
  declare function={
    f(\x,\k)=(1-abs(\x)^(\k))^(1/\k);
  },
}

\pgfplotsset{
  setup/.style={
    very thick,
    width=5cm,
    domain=-2:2, 
    samples=1001, 
    -,
    unbounded coords=jump,
    no marks,
    unit vector ratio*=1 1 1,
%    ticks=none,
    axis lines = middle,
    xmin = -1.2,
    xmax=1.4,
    ymin=-1.2,
    ymax=1.4,
    every axis y label/.style={
      at={(ticklabel* cs:1)},
      anchor=south,
    },
  },
  every non boxed x axis/.append style={
    axis line style=->
  },
  every non boxed y axis/.append style={
    axis line style=->
  },
}

\begin{document}
    % q=2
    \begin{tikzpicture}
      \begin{axis}[
        setup,
        ylabel={$q=2$},
        ]
        \addplot[blue] {f(x,2)};
        \addplot[blue] {-f(x,2)};
      \end{axis}
    \end{tikzpicture}
    \qquad 
%q=3
    \begin{tikzpicture}
      \begin{axis}[
        setup,
        ylabel={$q=3$},
        ]
        \addplot[red] {f(x,3)};
        \addplot[red] {-f(x,3)};
      \end{axis}
    \end{tikzpicture}
  \qquad    
    %q=4
    \begin{tikzpicture}
      \begin{axis}[
        setup,
        ylabel={$q=4$},
        ]
        \addplot[red] {f(x,4)};
        \addplot[red] {-f(x,4)};
      \end{axis}
    \end{tikzpicture}
  \qquad    
% %q=6
    \begin{tikzpicture}
      \begin{axis}[
        setup,
        ylabel={$q=6$},
        ]
        \addplot[red] {f(x,6)};
        \addplot[red] {-f(x,6)};
      \end{axis}
    \end{tikzpicture}
\end{document}

Answer 1

|x|>1我认为问题在于，如果和，函数不再是实数k>1。如果过滤掉有问题的值，就不会出现问题。

\documentclass[10pt]{standalone}
\usepackage{tikz,pgfplots}
\pgfplotsset{compat=1.15}
\usetikzlibrary{arrows.meta}

\tikzset{
  >={Latex[round]},
  declare function={
    f(\x,\k)=ifthenelse((1-abs(\x)^(\k))<0,0,(1-abs(\x)^(\k))^(1/\k));
  },
}

\pgfplotsset{
  setup/.style={
    very thick,
    width=5cm,
    domain=-2:2, 
    samples=1000, 
    -,
    unbounded coords=jump,
    no marks,
    unit vector ratio*=1 1 1,
%    ticks=none,
    axis lines = middle,
    xmin = -1.2,
    xmax=1.4,
    ymin=-1.2,
    ymax=1.4,
    every axis y label/.style={
      at={(ticklabel* cs:1)},
      anchor=south,
    },
  },
  every non boxed x axis/.append style={
    axis line style=->
  },
  every non boxed y axis/.append style={
    axis line style=->
  },
}

\begin{document}
    % q=2
    \begin{tikzpicture}
      \begin{axis}[
        setup,
        ylabel={$q=2$},
        ]
        \addplot[blue] ({ifthenelse(abs(x)>1,sign(x),x)},{f(x,2)});
        \addplot[blue] ({ifthenelse(abs(x)>1,sign(x),x)},{-f(x,2)});
      \end{axis}
    \end{tikzpicture}
    \qquad 
%q=3
    \begin{tikzpicture}
      \begin{axis}[
        setup,
        ylabel={$q=3$},
        ]
        \addplot[red] ({ifthenelse(abs(x)>1,sign(x),x)},{f(x,3)});
        \addplot[red] ({ifthenelse(abs(x)>1,sign(x),x)},{-f(x,3)});
      \end{axis}
    \end{tikzpicture}
  \qquad    
    %q=4
    \begin{tikzpicture}
      \begin{axis}[
        setup,
        ylabel={$q=4$},
        ]
        \addplot[red] ({ifthenelse(abs(x)>1,sign(x),x)},{f(x,4)});
        \addplot[red] ({ifthenelse(abs(x)>1,sign(x),x)},{-f(x,4)});
      \end{axis}
    \end{tikzpicture}
  \qquad    
% %q=6
    \begin{tikzpicture}
      \begin{axis}[
        setup,
        ylabel={$q=6$},
        ]
        \addplot[red] ({ifthenelse(abs(x)>1,sign(x),x)},{f(x,6)});
        \addplot[red] ({ifthenelse(abs(x)>1,sign(x),x)},{-f(x,6)});
      \end{axis}
    \end{tikzpicture}
\end{document}