-1

enter image description here

I would like to draw this diagram in tikz-cd. Specifically I would like the arrow to start 'from the top' of B here. I have looked at the example in the manual for tikz-cd, drawing the Snake Lemma, but it doesn't exactly explain anything well, and I have no idea what I'm doing regarding tikz in general. Is this easy at all to do?

To anyone asking why I would want to draw this diagram: I don't. I want to draw a diagram using similar arrows

2
  • 1
    Welcome to the TeX.SE. Would you like to draw or should we draw? :-) The arrows are of xy package and it has also the tips of tikz-cd package.
    – Sebastiano
    Feb 25 at 22:56
  • 1
    Did you say "Snake Lemma"? tex.stackexchange.com/q/3892/86 Feb 25 at 23:27
1

A proof of concept example, see

  • the user manual of tikz-cd v0.9f, sec. 3.1 "Tweaking to paths" and
  • pgfmanual v3.1.8b, sec. 14.13 "The To Path Operation".
\documentclass{article}
\usepackage{tikz-cd}

\begin{document}
\begin{tikzcd}
  A & B \arrow[dl,
          to path={ |- ([shift={(3ex,2ex)}] \tikztostart.north) 
                    |- ([shift={(0, -2ex)}] \tikztotarget.south)
                    -- (\tikztotarget)
          }] \\
  C & D
\end{tikzcd}
\end{document}

enter image description here

1

For fun, it is very simple with pstricks:

\documentclass{article}
\usepackage{pst-node}

\begin{document}

    \[ \begin{psmatrix}[colsep=1.7cm]
            [name=A] A & [name=B] B \\
            [name=C] C & [name=D] D
        \end{psmatrix}
        \psset{linewidth=0.6pt, arrows=->, arrowinset=0.12, labelsep=1pt, nodesep=2pt}
        \ncline{A}{B}\naput{f} \ncline{A}{C}\nbput{g}
        \ncline{B}{D}\naput{h} \ncline{C}{D}\nbput{k}
        \ncloop[angleA=90, angleB=-90, loopsize=0.6, linearc=0.1]{B}{C}
         \]

\end{document} 

enter image description here

2
  • Bernard, hi, you have \end{document} out of the code.
    – Sebastiano
    Feb 26 at 0:04
  • Oh! yes. Thanks!
    – Bernard
    Feb 26 at 0:16

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