绘制简单的决策树

Question

我找到了这个代码，但我只想绘制一个非常简单的决策树。我试图修改代码，但我无法摆脱其他分支。我只想要 S，然后是“上”和“下”两个选项。

\documentclass[12pt]{article}
\usepackage{tikz,forest}
\tikzset{
  treenode/.style = {shape=rectangle, rounded corners,
                     draw, align=center,
                     top color=white, bottom color=blue!20},
  root/.style     = {treenode, font=\Large, bottom color=red!30},
  env/.style      = {treenode, font=\ttfamily\normalsize},
  dummy/.style    = {circle,draw}
}
    \begin{document}
    \begin{tikzpicture}
      [
        grow                    = right,
        sibling distance        = 6em,
        level distance          = 10em,
        edge from parent/.style = {draw, -latex},
        every node/.style       = {font=\footnotesize},
        sloped
      ]
      \node [root] {S}
        child { node [env] {down}
          edge from parent node [below] {$40$} }
          child { node [env] {up}
          edge from parent node [below] {$20$} }
        child { node [dummy] {}
          child { node [dummy] {}
            child { node [env] {align\\flalign}
              edge from parent node [below] {at relation sign?} }
            child { node [env] {alignat}
              edge from parent node [above] {at several}
                               node [below] {places?} }
            child { node [env] {gather}
                    edge from parent node [above] {centered?} }
            edge from parent node [below] {aligned?} }
          child { node [env] {multline}
                  edge from parent node [above, align=center]
                    {first left,\\centered,}
                  node [below] {last right}}
                  edge from parent node [above] {$40$} };
    \end{tikzpicture}
    \end{document}

如果有人能解释一下这是如何工作的，我将不胜感激，因为我对 LaTeX 还很陌生。非常感谢！

Answer 1

tikz您可以在软件包文档（它是tikz安装的一部分，或者您可以在 CTAN 上找到它）中找到有关按软件包绘制树的最相关信息：钛钾Z 和 PGF 手册. 在部分21 让树木生长，第 333-342 页描述了基础知识，部分76 树图书馆 描述了trees库的使用（定义了两个新的增长函数）。

无论如何，在 MWE（最小工作示例）中，下面是一些非常简单的树的示例代码。前两个是用纯 绘制的tikz，最后一个使用forest。

\documentclass[12pt]{article}
\usepackage{tikz,forest}
\usetikzlibrary{arrows.meta}
\tikzset{% common styles of tikz pictures elements
  treenode/.style = {shape=rectangle, rounded corners,
                     draw, align=center, 
                     minimum height=2ex, text depth=0.25ex,
                     top color=white, bottom color=blue!20},
  root/.style     = {treenode, font=\Large\rmfamily, bottom color=red!30},
  env/.style      = {treenode, font=\ttfamily\normalsize},
}

    \begin{document}
Using `tikz` tree growing right:

    \begin{tikzpicture}[% local settings for tree
grow                     = right,
sibling distance         = 6em,
level distance           = 10em,
edge from parent/.style  = {draw, -latex},
every node/.append style = {font=\footnotesize},
sloped
                      ]
\node [root] {S}    % root node, here tree start, after it are childrens
    child { node [env] {down}
        edge from parent node [above] {Yes}}
    child { node [env] {up}
        edge from parent node [above] {No}} 
;
    \end{tikzpicture}

Using `tikz` tree growing down (default direction):

    \begin{tikzpicture}[% local settings for tree
%grow                     = right,
sibling distance         = 6em,
level distance           = 10em,
edge from parent/.style  = {draw, -latex},
every node/.append style = {font=\footnotesize},
sloped
                      ]
\node [root] {S}    % root node, here tree start, after it are childrens
    child { node [env] {down}
        edge from parent node [above] {Yes}}
    child { node [env] {up}
        edge from parent node [above] {No}}
;
    \end{tikzpicture}
    
Using `forest` growing down:   

    \begin{forest}
for tree = {% settings for elemts in tree
% nodes
    draw, rounded corners,
    top color=white, bottom color=blue!20,
    font = \ttfamily,
    minimum height=2ex, text depth = 0.25ex,
   anchor = north, 
% edges 
     edge = {-Stealth},
    s sep = 3em,
    l sep = 6em
            },
EL/.style = {% shortenes for Edge Label, defined as style
   before typesetting nodes={% edge labels positioning
where n=1{edge label/.wrap value={node[pos=0.5,anchor=east]{#1}}}% above left
         {edge label/.wrap value={node[pos=0.5,anchor=west]{#1}}}% above right
                            }
            }% end of EL
% tree body
[ S, root % rot is style defined in document preamble
    [down, EL=Yes]
    [up, EL=No]
]
    \end{forest}
    \end{document}

其生产成果为：

除了这种可能性之外，还存在其他可能性，如qtree包（tikz-qtree：使用 TikZ 制作更好的树） ETC。