Graphics, Figures & Tables ⇒ tikZ | Commutative Diagram

[gheorghebg]

Dear community,

I am using tikZ to draw mathematical commutative diagrams. I am struggling to draw a diagram as the image attached, but I don't really know how to draw the double diagonal line, the one labeled with H.

My code is

Code: Select all

\begin{tikzpicture}
\matrix (m) [matrix of math nodes, row sep=3em, column sep=3em, text height=1.5ex, text depth=0.25ex]
{ K & X  \\
  L & Y     \\ };
\path[->]
(m-1-1) edge (m-1-2)
(m-1-1) edge node[left] {$ i $} (m-2-1)
(m-1-2) edge node[right] {$ p $} (m-2-2)
(m-2-1) edge (m-2-2);
\path[dotted,->]
(m-2-1) edge (m-1-2);
\end{tikzpicture}

I thought about putting it as a label \Rightarrow for the diagonal dotted line L \to X, but then I get it horizontal on the right, instead of diagonal pointing down right. I feel like looking for a double diagonal line as a latex symbol is not the right way to solve the problem. Is there another way to draw the double line I want? Also, I may want to label this double line, so is it possible to draw it like a \path?

Thank you very much,
Bogdan

[localghost]

Please always provide a complete example that is compilable out of the box for everybody. It will be much easier then to test possible solutions without having to think about what is all necessary to get your code working.

The »calc« library of pgf/tikZ allows to calculate coordinates. This ways you can draw a path relative to the lower right matrix element.

Code: Select all

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{tikz}
\usetikzlibrary{calc,matrix}

\begin{document}
  \begin{tikzpicture}[>=stealth]
    \matrix (m) [
      matrix of math nodes,
      row sep=3em,
      column sep=3em,
      text height=1.5ex,
      text depth=0.25ex
    ] {
      K & X \\
      L & Y \\
    };
    \path[->]        (m-1-1) edge                   (m-1-2)
                     (m-1-1) edge node[left]  {$i$} (m-2-1)
                     (m-1-2) edge node[right] {$p$} (m-2-2)
                     (m-2-1) edge                   (m-2-2);
    \path[dotted,->] (m-2-1) edge (m-1-2);
    \draw[->,double] ($(m-2-2)+(-2em,2em)$) -- (m-2-2) node[midway,sloped,above] {\scriptsize $H$};
  \end{tikzpicture}
\end{document}

It might also be possible to draw the double line as intersection to the dotted line.


Thorsten

[Stefan Kottwitz]

Hi Bogdan,

Thorsten has already provided a nice way. Indeed, calculations with coordinates are generally useful. There's another approace, by placing a coordinate node and referring to that, without calculation.

Placing the center coordinate node, for example when drawing the dotted line:

Code: Select all

\path[dotted,->] (m-2-1) edge coordinate[midway] (center) (m-1-2);

Later we just use it, and shorten the arrow a bit:

Code: Select all

\draw[->,double,shorten <=0.5ex] (center) -- (m-2-2)
    node[midway,sloped,above] {\scriptsize $H$};

Complete code, based on your's and Thorsten's:

Code: Select all

\documentclass[11pt]{article}
\usepackage[T1]{fontenc}
\usepackage{tikz}
\usetikzlibrary{matrix}
\begin{document}
  \begin{tikzpicture}[>=stealth]
    \matrix (m) [
      matrix of math nodes,
      row sep=3em,
      column sep=3em,
      text height=1.5ex,
      text depth=0.25ex
    ] {
      K & X \\
      L & Y \\
    };
    \path[->]        (m-1-1) edge                   (m-1-2)
                     (m-1-1) edge node[left]  {$i$} (m-2-1)
                     (m-1-2) edge node[right] {$p$} (m-2-2)
                     (m-2-1) edge                   (m-2-2);
    \path[dotted,->] (m-2-1) edge coordinate[midway] (center) (m-1-2);
    \draw[->,double,shorten <=0.5ex] (center) -- (m-2-2)
        node[midway,sloped,above] {\scriptsize $H$};
  \end{tikzpicture}
\end{document}

Commutative Diagram

diagram.png (4.06 KiB) Viewed 4901 times

Stefan