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TikZ 入/出角度与贝塞尔控制

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TikZ 入/出角度与贝塞尔控制

在下图中，我希望两个段都具有当前位于左侧段的向上箭头，但我还希望两个段都具有当前位于右侧段的漂亮圆形。

在此处输入图片描述

MWE 代码：

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}

\begin{tikzpicture}
    \tikzstyle{smallnode}=[circle, inner sep=0mm, outer sep=0mm, minimum size=2mm, draw=black, fill=black];

    \node[smallnode, label={$i$}] (i)   at (0,0) {};
    \node[smallnode, label=below:{$j$}] (j)     at (1.5,-1) {};
    \node[smallnode, label={$k$}] (k)       at (1.5,0) {};
    \node[smallnode, label=below:{$l$}] (l)     at (0,-1) {};

    \draw (i) to[out=180, in=180, edge node={node [sloped,below] {$\leftarrow$}}] (l);
    \draw (k) .. controls ($ (k) +(2,1)$) and ($ (j) +(2,-1)$) .. (j);
\end{tikzpicture}

\end{document}

我的问题是，使用外角/内角（如左段所示）无法灵活地调整曲线的“圆度”，尽管它确实可以很容易地添加箭头。另一方面，使用贝塞尔曲线（如左段所示）似乎不允许使用边缘节点（或者允许吗？——我试过了

\draw (k) to[out=180, in=180, edge node={node [sloped,below] {$\leftarrow$}}] 
          .. controls ($ (k) +(2,1)$) and ($ (j) +(2,-1)$) .. (j);

和一些其他语法，但无法获得它）。

顺便说一句，我是 TikZ 的新用户，所以如果我在这段代码中做了其他愚蠢的事情，请告诉我！

答案1

我的最终代码基于@Manuel 的建议：

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}

\begin{tikzpicture}
    \tikzstyle{smallnode}=[circle, inner sep=0mm, outer sep=0mm, minimum size=2mm, draw=black, fill=black];

    \node[smallnode, label={$i$}] (i)   at (0,0) {};
    \node[smallnode, label=below:{$j$}] (j)     at (1.5,-1) {};
    \node[smallnode, label={$k$}] (k)       at (1.5,0) {};
    \node[smallnode, label=below:{$l$}] (l)     at (0,-1) {};

    \draw (i) to[out=150, in=210, looseness=4, edge node={node [sloped,below] {$\leftarrow$}}] (l);
    \draw (k) to[out=30, in=-30, looseness=4, edge node={node [sloped,above] {$\leftarrow$}}] (j);
\end{tikzpicture}

\end{document}

结果：

在此处输入图片描述

答案2

您始终可以在路径上放置一个节点并为其附加一些标签：

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}

\begin{document}

\begin{tikzpicture}
    \tikzstyle{smallnode}=[circle, inner sep=0mm, outer sep=0mm, minimum size=2mm, draw=black, fill=black];

    \node[smallnode, label={$i$}] (i)   at (0,0) {};
    \node[smallnode, label=below:{$j$}] (j)     at (1.5,-1) {};
    \node[smallnode, label={$k$}] (k)       at (1.5,0) {};
    \node[smallnode, label=below:{$l$}] (l)     at (0,-1) {};

    \draw (i) to[out=180, in=180, edge node={node [sloped,below] {$\leftarrow$}}] (l);
    \draw (k) .. controls ($ (k) +(2,1)$) and ($ (j) +(2,-1)$) .. (j) node[pos=0.5, inner sep=-1pt, label=right:{$\uparrow$}] {};
\end{tikzpicture}

\end{document}

在此处输入图片描述

答案3

这是 Metapost 版本，用于比较。我将两条曲线定义为path变量，这样我就可以使用point x of y符号在路径上的合适点放置标签。

在此处输入图片描述

prologues := 3;
outputtemplate := "%j%c.eps";

beginfig(1);

u = 1/2cm;
z1 = -z2 = (-3/2u,+u);
z3 = -z4 = (+3/2u,+u);

path h[];
h1 = z2 {dir -30} .. {dir 210} z3;
h2 = z4 {dir 210} .. {dir -30} z1;

draw h1; 
draw h2; 

label.rt (btex $\uparrow$ etex, point 0.5 of h1);
label.lft(btex $\uparrow$ etex, point 0.5 of h2);

dotlabel.top(btex $i$ etex, z1);
dotlabel.bot(btex $j$ etex, z2);
dotlabel.top(btex $k$ etex, z3);
dotlabel.bot(btex $l$ etex, z4);

endfig;
end.

subpath但是，你可以通过将部分的任意部分稍微向侧面移动来绘制更性感的箭头，就像这样：

在此处输入图片描述

prologues := 3;
outputtemplate := "%j%c.eps";

beginfig(2);
u = 1/2cm;

z1 = -z2 = (-3/2u,+u);
z3 = -z4 = (+3/2u,+u);

path h[];
h1 = z2 {dir -30} .. {dir 210} z3;
h2 = z4 {dir 210} .. {dir -30} z1;

draw h1; 
draw h2; 

drawarrow subpath (0.4,0.6) of h1 shifted 5 right;
drawarrow subpath (0.4,0.6) of h2 shifted 5 left;

dotlabel.top(btex $i$ etex, z1);
dotlabel.bot(btex $j$ etex, z2);
dotlabel.top(btex $k$ etex, z3);
dotlabel.bot(btex $l$ etex, z4);

endfig;
end.

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