How can I draw an Inference Network diagram?

Question

I want to build a tree diagram like this one:

I tried with forest package but I got stuck trying to connect two different blue boxes to a grey one.

Here it is what I tried with a more simple example trying to connect R2 and R4 with the same F node:

\begin{forest}
  for tree={
    draw=none,
    edge={-},
    l sep+=7.5pt,
    grow'=180, 
    anchor=north, 
  },
  [I
  [R3
      [C 
        [R1 [A] [B]] 
        [R2 [D] [E] [F]]
    ]
      [H 
        [R4 [F] ]
    ]
    ]
  ]
\end{forest}

I want to connect R2 and R4 nodes to the same F node :/

Maybe I can't do that with forest...

Welcome. I'm sure the forest pros can create such a diagram with forest (mathematically it is a tree after all), though I would use TikZ-CD (i.e. a matrix of nodes and edges) since it is so well structured. How complex will your diagrams get? — Qrrbrbirlbel, Jun 17 '23 at 01:17
@Qrrbrbirlbel diagrams can't get much complex but, for example, I could have more than 3 nodes (H,Z,X,Y...) conected to R_4 (always from top). Also, several R_x could be conected to one X (M,V,T,...) node. — felpud0, Jun 17 '23 at 11:43
@Qrrbrbirlbel I thought trees had to have single root nodes? Certainly they do in logic tableaux. (The other kind of tree in logic has a single terminal.) To do this in forest you have to use a fake root node, which is a bit fiddly because of the spacing. And then you have to hack the two-parent thing. — cfr, Jun 26 '23 at 20:01
@cfr Even if it were undirected it contains no cycles so any of them could be the root. But my studies of graph theory are well in the past. The edge direction shouldn't be of concern for TikZ/Forest since that is just a drawing and not a logical thing. — Qrrbrbirlbel, Jun 26 '23 at 20:15
@Qrrbrbirlbel I forgot there were trees in graph theory (about which I know nothing except a little from the TikZ manual). The direction of arrows isn't a concern for forest, but the structure is. forest draws trees in which children have exactly one parent and all nodes are either the root node of descendants of the root. You can fake other structures, but you need hacks of various kinds. (Which is why Gonzalo Medina uses two trees rather than one in that answer and combines them in a third tikzpicture.) — cfr, Jun 26 '23 at 20:26

score 9 · Accepted Answer · answered Jun 17 '23 at 02:09

Here's how I'd do it with a matrix using TikZ-CD since your diagram is so well structured.

Code

\documentclass[tikz]{standalone}
\usetikzlibrary{angles, cd}
\tikzset{% helpful styles
  odd rows/.style={/tikz/every odd row/.append style={nodes={#1}}},
  even rows/.style={/tikz/every even row/.append style={nodes={#1}}},
  labels/.style={/tikz/every label/.append style={#1}}}
\tikzcdset{% shortcuts to insert coordinate at start end end
  ms/.style={/tikz/every to/.append style={/tikz/edge node={coordinate[at start](#1)}}},
  me/.style={/tikz/every to/.append style={/tikz/edge node={coordinate[at end](#1)}}},
  mse/.style args={#1:#2}{ms={#1}, me={#2}}}
\begin{document}
\begin{tikzcd}[
  /tikz/labels={minimum size=+1pt, font=\footnotesize},% minimum size to reset
  /tikz/every label quotes/.append style={execute at begin node={FC={}}},
  start anchor=south, end anchor=north,
  cells={nodes={rounded corners, draw, thick}},
  arrows=-Stealth,
  column sep={5em,between origins}, row sep={5em,between origins},
  odd rows={
    fill=gray!50, minimum width=4em, minimum height=2em,
    labels={red!75!black, label position=north}},
  even rows={
    fill=green!50!blue!50, minimum size=3em,
    labels={green!50!blue!50, label position=north east, anchor=north west}},
  execute at end picture={
    \foreach \a in {F--E--D, I--H--G} \pic[draw] {angle/.expanded=\a};}
]
 &     |["0.6"]| C \dar
   & & |["0.5"]| H \dar & \\
 &   |[" 1  "]| R_3 \drar
 & & |["-0.4"]| R_4 \dlar \\
         |["0.6"]| P \drar[mse=D:E]
 & &               T \dlar[ms=F]\drar[mse=G:H]
     & & |["0.3"]| B \dlar[ms=I]\\
 &     |["0.9"]| R_1 \dar
   & & |["0.6"]| R_2 \dar \\
 & M & & V
\end{tikzcd}
\end{document}

Output

Definitely a more natural approach IMNSHO. – cfr Jun 26 '23 at 20:04 — cfr, Jun 26 '23 at 20:04

score 5 · Answer 2 · answered Jun 17 '23 at 10:49

Welcome to TeX.SE!!

Another approach, this one based in \pics. I made two \pics, one for each type of node. This way we can place the nodes and their labels with the same instruction. As the gray nodes can need or not the red label 'FC', I'm using the conditional \ifblank from etoolbox package.

The code:

\documentclass[tikz,border=1.618mm]{standalone}
\usepackage{etoolbox} % for \ifblank
\tikzset
{% 
   pics/gray node/.style 2 args={code=%
   {
      \node[draw,fill=gray!50,rounded corners,minimum width=1.3cm,minimum height=0.5cm] (aux) {$#1$};
      \ifblank{#2}{}{\node[red] at (0,0.5) {\small$FC=#2$};}
      \coordinate (-N) at (aux.north);
      \coordinate (-S) at (aux.south);
   }},
   pics/teal node/.style 2 args={code=%
   {
      \node[draw,fill=teal!50,rounded corners,minimum size=1.3cm] (aux) {$#1$};
      \node[teal,right] at (0.6,0.5) {\small$FC=#2$};
      \coordinate (-N) at (aux.north);
      \coordinate (-S) at (aux.south);
   }},
}
\begin{document}
\begin{tikzpicture}[font=\small,>=stealth]
  \pic (AL) at  (-2,4) {gray node={C}{0.6}};
  \pic (AR) at   (2,4) {gray node={H}{0.5}};
  \pic (BL) at  (-2,2) {teal node={R_3}{1}};
  \pic (BR) at   (2,2) {teal node={R_4}{-0.4}};
  \pic (CL) at  (-4,0) {gray node={P}{0.6}};
  \pic (T)  at   (0,0) {gray node={T}{}};
  \pic (CR) at   (4,0) {gray node={B}{0.3}};
  \pic (DL) at (-2,-2) {teal node={R_1}{0.9}};
  \pic (DR) at  (2,-2) {teal node={R_2}{0.6}};
  \pic (EL) at (-2,-4) {gray node={M}{}};
  \pic (ER) at  (2,-4) {gray node={V}{}};
  \foreach\i in {L,R}% left, right
  {
    \draw[->] (A\i-S) -- (B\i-N);
    \draw[->] (B\i-S) -- (T-N);
    \draw[->] (C\i-S) -- (D\i-N);
    \draw[->]   (T-S) -- (D\i-N);
    \draw[->] (D\i-S) -- (E\i-N);
    \begin{scope}
      \clip (C\i-S) -- (D\i-N) -- (T-S) -- cycle;
      \draw (D\i-N) circle (0.5);
    \end{scope}
  }
\end{tikzpicture}
\end{document}

How can I draw an Inference Network diagram?

2 Answers2

Code

Output