thank you for the tipp! I’ve corrected it above. I have compiled your sequence in order to see it and further to post it here as well:

Stefan

$\xymatrix{H_k(C_*)\ar[r]^{H_k(i_*)}& H_k(D_*)\ar[r]^{H_k(q_*)} & H_k(E_*) \ar @{->} `r/8pt[d] `/10pt[l]^\partial `^dl[ll] `^r/3pt[dll] [dll] \\ H_{k-1}(C_*)\ar[r]\ar[r]^{H_{k-1}(i_*)} & H_{k-1}(D_*)\ar[r]^{H_{k-1}(q_*)} & H_{k-1}(E_*)} $

Markus

I really appreciated your post. However need to have access to the options field of the edge command, e.g., for changing the style of my arrow tips. What I discovered is that this has a very simple solution. I just had to change the key handler /.code to the key handler /.code 2 args, that supports two arguments:

\tikzset{join/.code 2 arg=\tikzset{after node path={%
\ifx\tikzchainprevious\pgfutil@empty\else(\tikzchainprevious)%
edge[#1]#2(\tikzchaincurrent)\fi}}}

The first argument are the edge options and the second argument is the node command, corresponding to the sintax join={edge options}{node[options] {label}}.

Pedro

you could put the tikzpicture environment into an equation environment to get it numbered. Perhaps consider modifying the baseline of the tikz picture to position the equation tag at the center like

\begin{equation}
\begin{tikzpicture}[baseline=(current
    bounding box.center)]
...
\end{tikzpicture}
\end{equation}

Stefan

http://www.fauskes.net/nb/introducing-dot2texi

Alex

thank you for posting your comment. I’ve written above why I’m using TikZ instead of xymatrix/xypic. I’ve used xypic earlier, it’s a great tool and still recommendable. There could be advantages using a general purpose tool like TikZ, for instance if you want to combine it with other features, like overlays within a beamer presentation.
If just diagrams are considered xypic would be enough. My posting above is aimed at TikZ users, discussing production of diagrams without having to learn the xypic syntax.

Stefan