在一个图中拼接几个pgfplots轴

Question

我正在尝试制作磁滞回线样式的图形，并希望跳过图形实际上没有演变的一些 x 值。为此，我尝试将 3 个轴拼接在一起，每个轴都包含整体数据集的一部分。

MWE 如下：

\documentclass[]{standalone}

\usepackage{pgfplots}
\usepackage{tikz}

\usetikzlibrary{positioning}

\begin{document}

\newcommand\Xa{-7.5}
\newcommand\Xb{-6}
\newcommand\Xc{-1.5}
\newcommand\Xd{1.5}
\newcommand\Xe{6}
\newcommand\Xf{7.5}

\begin{tikzpicture}
\begin{axis}[%
name = mid,
unit vector ratio*=2 1 2,
xmin=\Xc,
xmax=\Xd,
xlabel={X label},
ymin=-4,
ymax=4,
axis background/.style={fill=white},
hide y axis
]
\addplot [color=red,solid,mark=asterisk,mark options={solid},forget plot, restrict x to domain=\Xc:\Xd]
 table[]{-1.5 -4
1.5 4
};

\node [inner sep=0,outer sep=0](midleft) at (axis cs:\Xc, -4) {};
\node [inner sep=0,outer sep=0](midright) at (axis cs:\Xd, -4) {};
\end{axis}

\begin{axis}[%
at={(mid.outer west)},anchor=outer east,
unit vector ratio*=2 1 2,
xmin=\Xa,
xmax=\Xb,
xlabel={\vphantom{X label}},
xtick={-7, -6},
ymin=-4,
ymax=4,
ylabel={Y label},
axis background/.style={fill=white},
axis y line*=left
]

\addplot [color=red,solid,mark=asterisk,mark options={solid},forget plot, restrict x to domain=\Xa:\Xb]
 table[]{-7 -4
-6 -4
};

\node [inner sep=0,outer sep=0](leftright) at (axis cs:\Xb, -4) {};
\end{axis}

\begin{axis}[%
at={(mid.outer east)},anchor=outer west,
unit vector ratio*=2 1 2,
xmin=\Xe,
xmax=\Xf,
xlabel={\vphantom{X label}},
xtick={6,7},
ymin=-4,
ymax=4,
axis background/.style={fill=white},
axis y line*=right
]
\addplot [color=red,solid,mark=asterisk,mark options={solid},forget plot, restrict x to domain=\Xe:\Xf]
 table[]{6 4
7 4
};

\node [inner sep=0,outer sep=0](rightleft) at (axis cs:\Xe, -4) {};
\end{axis}

\draw [blue, thick] (leftright) -- (midleft);
\draw [blue, thick] (midright) -- (rightleft);

\end{tikzpicture}%

\end{document}

结果如下

如您所见，存在一些问题：首先，x 轴在三个轴之间没有对齐，两个外侧轴似乎对齐了，但与中间轴不对齐。我尝试使用 \vphanton x-label 来纠正这个问题，这有点帮助，但没有让它对齐。

第二，中心与右轴、中心与左轴的距离不相等。

最后，应该“延续” x 轴的蓝线（我计划用摆动“装饰”它们，以便清楚地表明它们不是连续的）没有到达节点位置，有一个微小的间隙，在 PDF 输出中可见。我尝试通过将内部和外部 sep 设置为 0 来纠正，这也有帮助，但并没有完全解决问题。

有人能帮忙解决这些问题吗？

Answer 1

您犯的主要“错误”是使用“ outer”锚点来对齐axis环境。请查看代码中的注释，以详细了解我的解决方案的工作原理。

% used PGFPlots v1.14
\documentclass[border=5pt]{standalone}
\usepackage{pgfplots}
    \usetikzlibrary{positioning}
    \pgfplotsset{
        % use `compat' level 1.3 or higher to use the improved positioning
        % of the axis labels
        compat=1.3,
        %
        % moved common axis options to this style
        my axis style/.style={
            unit vector ratio*=2 1 2,
%            % commented next line, because I don't know what it is good for
%            % in this context
%            axis background/.style={fill=white},
        },
        % moved common `\addplot' option to this style
        my addplot style/.style={
            color=red,
            solid,
            mark=asterisk,
            mark options={solid},
            forget plot,
        },
    }
\begin{document}
    \begin{tikzpicture}
            % moved this commands inside the tikzpicture environment so they
            % are first localized and second don't produce some whitespaces
            \newcommand\Xa{-7.5}
            \newcommand\Xb{-6}
            \newcommand\Xc{-1.5}
            \newcommand\Xd{1.5}
            \newcommand\Xe{6}
            \newcommand\Xf{7.5}
            % define the length which should be gap between the axis environments
            \pgfmathsetlengthmacro{\xShift}{5mm}
        \begin{axis}[
            name=mid,
            my axis style,
            %
            xmin=\Xc,
            xmax=\Xd,
            xlabel={X label},
            ymin=-4,
            ymax=4,
            hide y axis,
        ]
            \addplot [
                my addplot style,
                restrict x to domain=\Xc:\Xd,
            ] table {
                -1.5 -4
                1.5 4
            };
        \end{axis}
            % create coordinate where "left" axis should end
            % (don't use the "outer" anchors, because they depend on the
            %  axes and tick labels, whereas the "not-outer" anchors don't)
            \coordinate (A) at ([xshift=-\xShift] mid.south west);
        \begin{axis}[
            name=left,
            % use the created coordinate to place this axis environment
            % and use an appropriate anchor
            at={(A)},
            anchor=south east,
            my axis style,
            %
            xmin=\Xa,
            xmax=\Xb,
            xtick={-7, -6},
            ymin=-4,
            ymax=4,
            ylabel={Y label},
            axis y line*=left,
        ]
            \addplot [
                my addplot style,
                restrict x to domain=\Xa:\Xb
            ] table {
                -7 -4
                -6 -4
            };
        \end{axis}
            % create coordinate where the "right" axis should begin
            \coordinate (B) at ([xshift=\xShift] mid.south east);
        \begin{axis}[
            name=right,
            % same as for the "left" axis
            at={(B)},
            anchor=south west,
            my axis style,
            %
            xmin=\Xe,
            xmax=\Xf,
            xtick={6,7},
            ymin=-4,
            ymax=4,
            axis y line*=right,
        ]
            \addplot [
                my addplot style,
                restrict x to domain=\Xe:\Xf,
            ] table {
                6 4
                7 4
            };
        \end{axis}
            % also for the "blue lines" use the
            \draw [blue,thick] (mid.south west) -- (left.south east);
            \draw [blue,thick] (mid.south east) -- (right.south west);

            % this line is just to prove, that the three axis environments
            % are really perfectly aligned now
            \draw [green,very thin,dashed]
                (left.south west) rectangle (right.north east);
    \end{tikzpicture}
\end{document}