pgfplot 中的“更智能”轴箭头

Question

对于任何常见的 x>0，y>0 函数，pgfplot 中的标准轴箭头位置都很好

不幸的是，对于更多的负函数（域或范围），箭头有点奇怪（红色=我想要的）。

似乎可以手动设置箭头，如下所示pgfplots：y 轴箭头朝下

然而，如果能够让情节使用正确的箭头，那就太棒了自动！

我正在思考某种逻辑，例如：

• 如果 x 轴 >0，使用右箭头
• 如果 x 轴 <0，使用左箭头
• 如果 y 轴 >0，则使用顶部箭头
• 如果 y 轴小于 0，则使用底部箭头

但是我不知道该如何做，有人愿意帮忙吗？

平均能量损失

\documentclass{article}

\usepackage{pgfplots}
\usetikzlibrary{arrows.meta}

\pgfplotsset{
    no marks,axis lines=middle,
    inner axis line style={-{Latex[length=4mm]}}
}

\begin{document}

\begin{center}
    \begin{tikzpicture}
        \begin{axis}[domain=0:1]
            \addplot+{x};
        \end{axis}
    \end{tikzpicture}
\end{center}

\end{document}

Answer 1

我认为，这符合您的建议。iaxis样式会查看原点是位于轴边界的左侧/右侧/上方/下方，并相应地添加箭头。

\documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.16}
\usetikzlibrary{arrows.meta,calc}

\pgfplotsset{no marks,
    iaxis/.style={,axis lines=middle,
    inner axis line style={-},clip mode=individual,execute at end axis={
    \path[tips=proper] let \p1=($(rel axis cs:1,1)-(axis cs:0,0)$),
     \p2=($(axis cs:0,0)-(rel axis cs:0,0)$)
     in %\pgfextra{\typeout{\x1,\x2,\y1,\y2}}
     \ifdim\x1>0pt
      (axis cs:0,0) edge[-{Latex[length=4mm]}] ({rel axis cs:1,0} |- {axis cs:0,0})
     \fi
     \ifdim\x2>0pt
      (axis cs:0,0) edge[-{Latex[length=4mm]}] ({rel axis cs:0,0} |- {axis cs:0,0})
     \fi
     \ifdim\y1>0pt
      (axis cs:0,0) edge[-{Latex[length=4mm]}] ({rel axis cs:0,1} -| {axis cs:0,0})
     \fi
     \ifdim\y2>0pt
      (axis cs:0,0) edge[-{Latex[length=4mm]}] ({rel axis cs:0,0} -| {axis cs:0,0})
     \fi;
    }},
    every axis/.append style=iaxis
}

\begin{document}
\begin{tabular}{cc}
\begin{tikzpicture}
    \begin{axis}[domain=0:1]
        \addplot+{x};
    \end{axis}
\end{tikzpicture} &
\begin{tikzpicture}
    \begin{axis}[domain=0:1]
        \addplot+{-x};
    \end{axis}
\end{tikzpicture}\\
\begin{tikzpicture}
    \begin{axis}[domain=-1:0]
        \addplot+{x};
    \end{axis}
\end{tikzpicture} &
\begin{tikzpicture}
    \begin{axis}[domain=-1:0]
        \addplot+{-x};
    \end{axis}
\end{tikzpicture}\\
\begin{tikzpicture}
    \begin{axis}[domain=-1:1]
        \addplot+{-x};
    \end{axis}
\end{tikzpicture}
\end{tabular}
\end{document}

或者使用超出范围的箭头（这会改变轴对象的尺寸）。

\documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.16}
\usetikzlibrary{arrows.meta,calc}

\pgfplotsset{no marks,
    iaxis/.style={axis lines=middle,
    inner axis line style={-},clip mode=individual,execute at end axis={
    \path[tips=proper] let \p1=($(rel axis cs:1,1)-(axis cs:0,0)$),
     \p2=($(axis cs:0,0)-(rel axis cs:0,0)$)
     in %\pgfextra{\typeout{\x1,\x2,\y1,\y2}}
     \ifdim\x1>0pt
      (axis cs:0,0) edge[-{Latex[length=4mm]}] 
      ($({rel axis cs:1,0} |- {axis cs:0,0})+($(4mm,0)-(0,0)$)$)
     \fi
     \ifdim\x2>0pt
      (axis cs:0,0) edge[-{Latex[length=4mm]}] 
      ($({rel axis cs:0,0} |- {axis cs:0,0})+($(-4mm,0)-(0,0)$)$)
     \fi
     \ifdim\y1>0pt
      (axis cs:0,0) edge[-{Latex[length=4mm]}] 
      ($({rel axis cs:0,1} -| {axis cs:0,0})+($(0,4mm)-(0,0)$)$)
     \fi
     \ifdim\y2>0pt
      (axis cs:0,0) edge[-{Latex[length=4mm]}] 
      ($({rel axis cs:0,0} -| {axis cs:0,0})+($(0,-4mm)-(0,0)$)$)
     \fi;
    }},
    every axis/.append style=iaxis
}

\begin{document}
\begin{tabular}{cc}
\begin{tikzpicture}
    \begin{axis}[domain=0:1]
        \addplot+{x};
    \end{axis}
\end{tikzpicture} &
\begin{tikzpicture}
    \begin{axis}[domain=0:1]
        \addplot+{-x};
    \end{axis}
\end{tikzpicture}\\
\begin{tikzpicture}
    \begin{axis}[domain=-1:0]
        \addplot+{x};
    \end{axis}
\end{tikzpicture} &
\begin{tikzpicture}
    \begin{axis}[domain=-1:0]
        \addplot+{-x};
    \end{axis}
\end{tikzpicture}\\
\begin{tikzpicture}
    \begin{axis}[domain=-1:1]
        \addplot+{-x};
    \end{axis}
\end{tikzpicture}
\end{tabular}
\end{document}